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Plomp V, Wang XD, Kłos J, Dagdigian PJ, Lique F, Onvlee J, van de Meerakker SY. Imaging Resonance Effects in C + H 2 Collisions Using a Zeeman Decelerator. J Phys Chem Lett 2024; 15:4602-4611. [PMID: 38640083 PMCID: PMC11071073 DOI: 10.1021/acs.jpclett.3c03379] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2023] [Revised: 04/05/2024] [Accepted: 04/05/2024] [Indexed: 04/21/2024]
Abstract
An intriguing phenomenon in molecular collisions is the occurrence of scattering resonances, which originate from bound and quasi-bound states supported by the interaction potential at low collision energies. The resonance effects in the scattering behavior are extraordinarily sensitive to the interaction potential, and their observation provides one of the most stringent tests for theoretical models. We present high-resolution measurements of state-resolved angular scattering distributions for inelastic collisions between Zeeman-decelerated C(3P1) atoms and para-H2 molecules at collision energies ranging from 77 cm-1 down to 0.5 cm-1. Rapid variations in the angular distributions were observed, which can be attributed to the consecutive reduction of contributing partial waves and effects of scattering resonances. The measurements showed excellent agreement with distributions predicted by ab initio quantum scattering calculations. However, discrepancies were found at specific collision energies, which most likely originate from an incorrectly predicted quasi-bound state. These observations provide exciting prospects for further high-precision and low-energy investigations of scattering processes that involve paramagnetic species.
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Affiliation(s)
- Vikram Plomp
- Radboud
University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - Xu-Dong Wang
- Radboud
University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - Jacek Kłos
- University
of Maryland, Department of Physics,
Joint Quantum Institute, College
Park, Maryland 20742, United States of America
| | - Paul J. Dagdigian
- Johns
Hopkins University, Department of Chemistry, Baltimore, Maryland 21218, United States
of America
| | - François Lique
- Université
de Rennes, Institut de Physique
de Rennes, 263 avenue
du Général Leclerc, Rennes CEDEX 35042, France
| | - Jolijn Onvlee
- Radboud
University, Institute for Molecules and Materials, Heijendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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Dagdigian PJ. Interaction of methanol with molecular hydrogen: Ab initio potential energy surface and scattering calculations. J Chem Phys 2023; 159:114302. [PMID: 37712787 DOI: 10.1063/5.0170594] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Accepted: 08/28/2023] [Indexed: 09/16/2023] Open
Abstract
The potential energy surface (PES) describing the interaction of the methanol molecule with molecular hydrogen has been calculated by the use of the explicitly correlated coupled cluster method, including single, double, and (perturbative) triple excitations [CCSD(T)-F12a] and a correlation-consistent aug-cc-pVTZ basis, with the assumption of fixed molecular geometries. The computed points were fit to a functional form appropriate for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate coefficients. Stationary points on the PES were located, and the global minimum was found to have an energy equal to -254.7 cm-1 relative to the energy of the separated molecules. This PES was used in time-independent close coupling quantum scattering calculations to determine state-to-state cross sections and rate coefficients for rotational transitions within the A- and E-type nuclear spin torsional ground states.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Ben Khalifa M, Dagdigian PJ, Loreau J. Interaction of CH 3CN and CH 3NC with He: Potential Energy Surfaces and Low-Energy Scattering. J Phys Chem A 2022; 126:9658-9666. [PMID: 36534035 DOI: 10.1021/acs.jpca.2c06925] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Several nitrogen-bearing molecules, such as methyl cyanide (or acetonitrile, CH3CN) and methyl isocyanide (CH3NC) of interest here, have been observed in various astrophysical environments. The accurate modeling of their abundance requires the calculation of rate coefficients for their collisional excitation with species such as He atoms or H2 molecules at low temperatures. In this work we compute new three-dimensional potential energy surfaces for the CH3NC-He and CH3CN-He van der Waals complexes by means of the explicitly correlated coupled cluster approach with single, double and perturbative triple excitation CCSD(T)/F12a in conjunction with the aug-cc-pVTZ basis set. We find a global minimum with De = 55.10 and 58.61 cm-1 for CH3CN-He and CH3NC-He, respectively, while the dissociation energy D0 of the complexes are 18.64 and 18.65 cm-1, respectively. Low-energy scattering calculations of pure rotational (de-)excitation of CH3CN and CH3NC by collision with He atoms are carried out with the close-coupling method, and the collisional cross sections of ortho- and para-CH3NC and CH3CN are computed for kinetic energies up to 100 cm-1. While the PESs for both complexes are qualitatively similar, that of CH3NC-He is more anisotropic, leading to different propensity rules for rotational excitation. For CH3NC-He, we find that |Δj| = 1 transitions are dominant at low kinetic energy and a propensity rule that favors odd Δj transitions is observed, whereas for CH3CN the dominant cross sections are associated with transitions with |Δj| = 2. We expect that the findings of this study will be beneficial for astrophysical investigations as well as laboratory experiments.
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Affiliation(s)
- Malek Ben Khalifa
- KU Leuven, Department of Chemistry, Celestijnenlaan 200F, B-3001Leuven, Belgium
| | - Paul J Dagdigian
- The Johns Hopkins University, Department of Chemistry, Baltimore, Maryland21218-2685, United States
| | - Jérôme Loreau
- KU Leuven, Department of Chemistry, Celestijnenlaan 200F, B-3001Leuven, Belgium
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Dagdigian PJ. Theoretical Investigation of Rotationally Inelastic Collisions of OH( X2Π) with Hydrogen Atoms. J Chem Phys 2022; 157:104305. [DOI: 10.1063/5.0110724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
State-to-state cross sections and rate coefficients for transitions between rotational/fine- structure levels of OH(X2Π) induced by collisions with atomic hydrogen are reported in this work. The scattering calculations take into account the full open-shell character of the OH + H system and include the four potential energy surfaces (1A′, 1A′′, 3A′, 3A′′) that correlate with the OH(X2Π) + H(2S) asymptote. Three of these surfaces are repulsive, while the deep H2O well is present on one surface (1A′). The OH + H potential energy curves calculated by Alexander et al. [J. Chem. Phys. 121, 5221 (2004)] are employed in this work. Time independent quantum scattering calculations were performed using the quantum statistical method of Manolopoulos and co-workers [Chem. Phys. Lett. 343, 356 (2001)] because of the presence of the deep H2O well. The computed cross sections include contributions from direct scattering, as well formation and decay of a transient collision complex since the transient HO-H complex is expected to decay nonreactively. Rate coefficients for OH-H inelastic collisions are of interest for astrophysical applications.
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Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, Johns Hopkins University, United States of America
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Dagdigian PJ. The interaction of methylene with molecular hydrogen: potential energy surface and inelastic collisions. Mol Phys 2021. [DOI: 10.1080/00268976.2021.1953173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD, USA
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Pirlot P, Kalugina YN, Ramachandran R, Raffy G, Dagdigian PJ, Lique F. Collisional excitation of NH by H 2: Potential energy surface and scattering calculations. J Chem Phys 2021; 155:134303. [PMID: 34624970 DOI: 10.1063/5.0066161] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Collisional data for the excitation of NH by H2 are key to accurately derive the NH abundance in astrophysical media. We present a new four-dimensional potential energy surface (PES) for the NH-H2 van der Waals complex. The ab initio calculations of the PES were carried out using the explicitly correlated partially spin-restricted coupled cluster method with single, double, and perturbative triple excitations [RCCSD(T)-F12a] with the augmented correlation-consistent polarized valence triple zeta basis set. The PES was represented by an angular expansion in terms of coupled spherical harmonics. The global minimum corresponds to the linear structure with a well depth De = 149.10 cm-1. The calculated dissociation energy D0 is found to be 30.55 and 22.11 cm-1 for ortho-H2 and para-H2 complexes, respectively. These results are in agreement with the experimental values. Then, we perform quantum close-coupling calculations of the fine structure resolved excitation cross sections of NH induced by collisions with ortho-H2 and para-H2 for collisional energies up to 500 cm-1. We find strong differences between collisions induced by ortho-H2 and para-H2. Propensity rules are discussed. The cross sections are larger for fine structure conserving transitions than for fine structure changing ones, as predicted by theory. These new results should help in interpreting NH interstellar spectra and better constrain the abundance of NH in interstellar molecular clouds.
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Affiliation(s)
- Paul Pirlot
- University Rennes, CNRS, IPR (Institut de Physique de Rennes)-UMR 6251, F-35000 Rennes, France
| | - Yulia N Kalugina
- Institute of Spectroscopy, Russian Academy of Sciences, Fizicheskaya St. 5, 108840 Troitsk, Moscow, Russia
| | - Ragav Ramachandran
- LOMC-UMR 6294, CNRS-Université du Havre, 25 Rue Philippe Lebon, BP 1123, Le Havre, France
| | - Guillaume Raffy
- University Rennes, CNRS, IPR (Institut de Physique de Rennes)-UMR 6251, F-35000 Rennes, France
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - François Lique
- University Rennes, CNRS, IPR (Institut de Physique de Rennes)-UMR 6251, F-35000 Rennes, France
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Dagdigian PJ. Interaction of the HCO radical with molecular hydrogen: Ab initio potential energy surface and scattering calculations. J Chem Phys 2020; 152:224304. [PMID: 32534536 DOI: 10.1063/5.0012033] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The potential energy surface describing the interaction of the HCO radical with molecular hydrogen has been computed through explicitly correlated coupled cluster calculations including single, double, and (perturbative) triple excitations [RCCSD(T)-F12a], with the assumption of fixed molecular geometries. The computed points were fit to an analytical form suitable for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate coefficients. Since the spin-rotation splittings in HCO are small, cross sections for fine-structure resolved transitions are computed with electron-spin free T matrix elements through the recoupling technique usually employed to determine hyperfine-resolved cross sections. Both spin-free and fine-structure resolved state-to-state cross sections for rotationally inelastic transitions are presented and discussed.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Dagdigian PJ. Interaction of the H 2S molecule with molecular hydrogen: Ab initio potential energy surface and scattering calculations. J Chem Phys 2020; 152:074307. [PMID: 32087660 DOI: 10.1063/1.5144604] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The potential energy surface describing the interaction of H2S with molecular hydrogen has been computed through explicitly correlated coupled cluster calculations including single, double, and (perturbative) triple excitations [CCSD(T)-F12a], with the assumption of fixed molecular geometries. The computed points were fit to an analytical form suitable for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate coefficients. Representative sets of energy dependent state-to-state rotationally inelastic cross sections and rate coefficients are presented and discussed.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Dagdigian PJ. Quantum statistical study of the C + + OH → CO + H +/CO + + H reaction: Reaction rate and product branching ratio at interstellar temperatures. J Chem Phys 2019. [DOI: 10.1063/1.5115992] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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10
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Dagdigian PJ. Interaction of the SH+ ion with molecular hydrogen: Ab initio potential energy surface and scattering calculations. J Chem Phys 2019; 150:084308. [DOI: 10.1063/1.5087701] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Abstract
The chemistry of fluorine in the interstellar medium is particularly simple, with only a few key species and important reactions. Of the latter, the rate of the reaction of C+ ions with HF is not well established but is one of the key reactions that sets the relative abundance of HF and the CF+ ion, the two fluorine-bearing species that have been observed in interstellar clouds. The C+ + HF → CF+ + H reaction proceeds through a deeply bound HCF+ well. In this work, statistical methods, namely, the statistical adiabatic channel method originally developed by Quack and Troe and the quantum statistical method of Manolopoulos and co-workers, are applied to compute the total cross section as a function of energy for this reaction. This reaction proceeds on the ground 12 A' potential energy surface (PES), and there are also two non-reactive PES's, 12 A″ and 22 A', correlating with the C+(2 P 1/2,3/2) + HF reactants. Two sets of scattering calculations were carried out, namely, a single-surface calculation on the 12 A' PES and the one in which all three PES's and the spin-orbit splitting of C+ are included in the description of the entrance channel. In the latter, reactivity of the spin-orbit excited 2 P 3/2 level can be computed, and not just assumed to be zero, as in the single-state adiabatic approximation.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
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Nuñez-Reyes D, Kłos J, Alexander MH, Dagdigian PJ, Hickson KM. Experimental and theoretical investigation of the temperature dependent electronic quenching of O(1D) atoms in collisions with Kr. J Chem Phys 2018; 148:124311. [DOI: 10.1063/1.5021885] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Affiliation(s)
- Dianailys Nuñez-Reyes
- Institut des Sciences Moléculaires, Université de Bordeaux, UMR 5255, F-33400 Talence, France
- CNRS, Institut des Sciences Moléculaires, UMR 5255, F-33400 Talence, France
| | - Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Kevin M. Hickson
- Institut des Sciences Moléculaires, Université de Bordeaux, UMR 5255, F-33400 Talence, France
- CNRS, Institut des Sciences Moléculaires, UMR 5255, F-33400 Talence, France
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Abstract
The potential energy surface (PES) describing the interaction of the ethynyl (C2H) radical in its ground X̃2Σ+ electronic state with molecular hydrogen has been computed through restricted coupled cluster calculations including single, double, and (perturbative) triple excitations [RCCSD(T)], with the assumption of fixed molecular geometries. The computed points were fit to an analytical form suitable for time-independent quantum scattering calculations of rotationally inelastic cross sections and rate constants. A representative set of energy dependent state-to-state cross sections is presented and discussed. The PES and cross sections for collisions of H2(j = 0) are compared with a previous study [F. Najar et al., Chem. Phys. Lett. 614, 251 (2014)] of collisions of C2H with H2 treated as a spherical collision partner. Good agreement is found between the two sets of calculations when the H2 molecule in the present calculation is spherically averaged.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Abstract
We report calculations of state-to-state cross sections for collision-induced rotational transitions of CH(X2Π) with atomic hydrogen. These calculations employed the four adiabatic potential energy surfaces correlating CH(X2Π) + H(2S), computed in this work through the multi-reference configuration interaction method [MRCISD + Q(Davidson)]. Because of the presence of deep wells on three of the potential energy surfaces, the scattering calculations were carried out using the quantum statistical method of Manolopoulos and co-workers [Chem. Phys. Lett. 343, 356 (2001)]. The computed cross sections included contributions from only direct scattering since the CH2 collision complex is expected to decay predominantly to C + H2. Rotationally energy transfer rate constants were computed for this system since these are required for astrophysical modeling.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Kłos J, Alexander MH, Dagdigian PJ. The interaction of NO(X2Π) with H2: Ab initio potential energy surfaces and bound states. J Chem Phys 2017; 146:114301. [DOI: 10.1063/1.4977992] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Abstract
We report calculations of state-to-state cross sections for collision-induced rotational transitions of CH(X2Π) with molecular hydrogen. These calculations employed the diabatic matrix elements of the interaction potential determined by Dagdigian [J. Chem. Phys. 145, 114301 (2016)], which employed the multi-reference configuration-interaction method [MRCISD+Q(Davidson)]. Because of the presence of a deep well on the lower potential energy surface, the scattering calculations were carried out using the quantum statistical method of Manolopoulos and co-workers [Chem. Phys. Lett. 343, 356 (2001)]. The computed cross sections included contributions from direct scattering, as well as from the formation and decay of a collision complex. The magnitude of latter contribution was found to decrease significantly with increasing collision energy. Rotationally energy transfer rate constants were computed for this system since these are required for astrochemical modeling.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Mick Warehime
- Chemical Physics Program, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
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Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, United States
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Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Dagdigian PJ. Erratum: “Accurate transport properties for H–CO and H–CO 2” [J. Chem. Phys. 143, 054303 (2015)]. J Chem Phys 2015; 143:159902. [DOI: 10.1063/1.4934219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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Boyson TK, Dagdigian PJ, Pavey KD, FitzGerald NJ, Spence TG, Moore DS, Harb CC. Real-time multiplexed digital cavity-enhanced spectroscopy. Opt Lett 2015; 40:4560-4562. [PMID: 26421581 DOI: 10.1364/ol.40.004560] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Cavity-enhanced spectroscopy is a sensitive optical absorption technique but one where the practical applications have been limited to studying small wavelength ranges. This Letter shows that wideband operation can be achieved by combining techniques usually reserved for the communications community with that of cavity-enhanced spectroscopy, producing a multiplexed real-time cavity-enhanced spectrometer. We use multiple collinear laser sources operating asynchronously and simultaneously while being detected on a single photodetector. This is synonymous with radio frequency (RF) cellular systems in which signals are detected on a single antenna but decoded uniquely. Here, we demonstrate results with spectra of methyl salicylate and show parts-per-billion per root hertz sensitivity measured in real-time.
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Garofalo LA, Smith MC, Dagdigian PJ, Kłos J, Alexander MH, Boering KA, Lin JJM. Electronic quenching of O((1)D) by Xe: Oscillations in the product angular distribution and their dependence on collision energy. J Chem Phys 2015; 143:054307. [PMID: 26254653 DOI: 10.1063/1.4927705] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The dynamics of the O((1)D) + Xe electronic quenching reaction was investigated in a crossed beam experiment at four collision energies. Marked large-scale oscillations in the differential cross sections were observed for the inelastic scattering products, O((3)P) and Xe. The shape and relative phases of the oscillatory structure depend strongly on collision energy. Comparison of the experimental results with time-independent scattering calculations shows qualitatively that this behavior is caused by Stueckelberg interferences, for which the quantum phases of the multiple reaction pathways accessible during electronic quenching constructively and destructively interfere.
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Affiliation(s)
- Lauren A Garofalo
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Mica C Smith
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Kristie A Boering
- Department of Chemistry, University of California, Berkeley, California 94720, USA
| | - Jim Jr-Min Lin
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei 10617, Taiwan
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Dagdigian PJ, Alexander MH, Kłos J. Theoretical investigation of the dynamics of O((1)D→(3)P) electronic quenching by collision with Xe. J Chem Phys 2015; 143:054306. [PMID: 26254652 DOI: 10.1063/1.4927704] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present the quantum close-coupling treatment of spin-orbit induced transitions between the (1)D and (3)P states of an atom in collisions with a closed-shell spherical partner. In the particular case of O colliding with Xe, we used electronic structure calculations to compute the relevant potential energy curves and spin-orbit coupling matrix elements. We then carried out quantum scattering calculations of integral and differential quenching cross sections as functions of the collision energy. The calculated differential cross sections for electronic quenching are in reasonable agreement with measurements [Garofalo et al., J. Chem. Phys. 143, 054307 (2015)]. The differential cross sections exhibit pronounced oscillations as a function of the scattering angle. By a semiclassical analysis, we show that these oscillations result from quantum mechanical interference between two classical paths.
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Affiliation(s)
- Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
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Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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van der Avoird A, Loreau J, Alexander MH, van de Meerakker SYT, Dagdigian PJ. Resonances in rotationally inelastic scattering of NH3 and ND3 with H2. J Chem Phys 2015; 143:044312. [PMID: 26233134 DOI: 10.1063/1.4927074] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Ad van der Avoird
- Institute for Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
| | - Jérôme Loreau
- Service de Chimie Quantique et Photophysique C. P. 160/09, Université Libre de Bruxelles (ULB), 50 Ave. F. D. Roosevelt, 1050 Brussels, Belgium
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | | | - Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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26
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Abstract
Frequency-modulated laser transient absorption has been used to monitor the ground-state rotational energy-transfer rates of CN radicals in a double-resonance, depletion recovery experiment. When a pulsed laser is used to burn a hole in the equilibrium ground-state population of one rotational state without velocity selection, the population recovery rate is found to depend strongly on the Doppler detuning of a narrow-band probe laser. Similar effects should be apparent for any relaxation rate process that competes effectively with velocity randomization. Alternative methods of extracting thermal rate constants in the presence of these non-thermal conditions are evaluated. Total recovery rate constants, analogous to total removal rate constants in an experiment preparing a single initial rotational level, are in good agreement with quantum scattering calculations, but are slower than previously reported experiments and show qualitatively different rotational state dependence between Ar and He collision partners. Quasi-classical trajectory studies confirm that the differing rotational state dependence is primarily a kinematic effect.
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Affiliation(s)
- Damien Forthomme
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Michael L Hause
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Hua-Gen Yu
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
| | - Paul J Dagdigian
- ‡Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Trevor J Sears
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States.,§Department of Chemistry, Stony Brook University, Stony Brook, New York 11794-3400, United States
| | - Gregory E Hall
- †Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, United States
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Tkáč O, Saha AK, Loreau J, Ma Q, Dagdigian PJ, Parker DH, van der Avoird A, Orr-Ewing AJ. Rotationally inelastic scattering of ND3with H2as a probe of the intermolecular potential energy surface. Mol Phys 2015. [DOI: 10.1080/00268976.2015.1059958] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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28
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Schewe HC, Vanhaecke N, Kłos J, Alexander MH, van de Meerakker SYT, Meijer G, van der Avoird A, Dagdigian PJ. Rotationally inelastic scattering of OH by molecular hydrogen: Theory and experiment. J Chem Phys 2015; 142:204310. [DOI: 10.1063/1.4921562] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- H. Christian Schewe
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Nicolas Vanhaecke
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
- Laboratoire Aimé Cotton-UMR 9188 CNRS, Université Paris-Sud 11 and Ecole Normale Supérieure Cachan, 91405 Orsay, France
| | - Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Sebastiaan Y. T. van de Meerakker
- Molecular and Laser Physics, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6265 AJ Nijmegen, The Netherlands
| | - Gerard Meijer
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany
| | - Ad van der Avoird
- Theoretical Chemistry, Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6265 AJ Nijmegen, The Netherlands
| | - Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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29
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Abstract
The rotationally inelastic scattering of methyl radical with Ar and N2 is examined at collision energies of 330 ± 25 cm(-1) and 425 ± 50 cm(-1), respectively. Differential cross sections (DCSs) were measured for different final n' rotational levels (up to n' = 5) of the methyl radicals, averaged over k' sub-levels, using a crossed molecular beam machine with velocity map imaging. For Ar as a collision partner, we present a newly constructed ab initio potential energy surface and quantum mechanical scattering calculations of state-resolved DCSs. These computed DCSs agree well with the measurements. The DCSs for both Ar and N2 collision partners are strongly forward peaked for all spectroscopic lines measured. For scattering angles below 60°, the theoretical CD3-Ar DCSs show diffraction oscillations that become less pronounced as n' increases, but these oscillations are not resolved experimentally. Comparisons are drawn with our recently reported DCSs for scattering of methyl radicals with He atoms.
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Affiliation(s)
- Ondřej Tkáč
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Qianli Ma
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Martin Stei
- Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria
| | - Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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30
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Ma L, Dagdigian PJ, Alexander MH. Theoretical investigation of the relaxation of the bending mode of CH₂(X̃) by collisions with helium. J Chem Phys 2014; 141:214305. [PMID: 25481142 DOI: 10.1063/1.4902004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We have earlier determined the dependence on the bending angle of the interaction of the methylene radical (CH2) in its X̃³B₁ state with He [L. Ma, P. J. Dagdigian, and M. H. Alexander, J. Chem. Phys. 136, 224306 (2012)]. By integration over products of the bending vibrational wave function, in a quantum close-coupled treatment we have calculated cross sections for the ro-vibrational relaxation of CH 2(X̃). Specifically, we find that cross sections for a loss of one vibrational quantum (v(b) = 2 → 1 and 1 → 0) are roughly two orders of magnitude smaller, and those for a loss of two vibrational quanta (v(b) = 2 → 0) four orders of magnitude smaller, than those for pure rotational relaxation. In addition, no clear cut dependence on the energy gap is seen.
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Affiliation(s)
- Lifang Ma
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
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31
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Kłos J, Alexander MH, van der Avoird A, Dagdigian PJ. The interaction of OH(X2Π) with H2:Ab initiopotential energy surfaces and bound states. J Chem Phys 2014; 141:174309. [DOI: 10.1063/1.4900478] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Jacek Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
- Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Ad van der Avoird
- Theoretical Chemistry, IMM, Radboud University Nijmegen, Heyendaalseweg 135, 6265 AJ Nijmegen, The Netherlands
| | - Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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32
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Ma L, Alexander MH, Dagdigian PJ. Theoretical investigation of intersystem crossing between the ã¹A₁ and X³B₁ states of CH₂ induced by collisions with helium. J Chem Phys 2014; 141:064312. [PMID: 25134576 DOI: 10.1063/1.4892377] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Collisional energy transfer between the ground (X³B₁) and first excited (ã¹A₁) states of CH2 is facilitated by strong mixing of the rare pairs of accidentally degenerate rotational levels in the ground vibrational manifold of the [Formula: see text] state and the (020) and (030) excited bending vibrational manifolds of the X state. The simplest model for this process involves coherent mixing of the scattering T-matrix elements associated with collisional transitions within the unmixed ã and X states. From previous calculations in our group, we have determined cross sections and room-temperature rate constants for intersystem crossing of CH2 by collision with He. These are used in simulations of the time dependence of the energy flow, both within and between the X and ã vibronic manifolds. Relaxation proceeds through three steps: (a) rapid equilibration of the two mixed-pair levels, (b) fast relaxation within the ã state, and (c) slower relaxation among the levels of the X state. Collisional transfer between the fine-structure levels of the triplet (X) state is very slow.
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Affiliation(s)
- Lifang Ma
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
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33
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Affiliation(s)
- Paul J. Dagdigian
- Department
of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, United States
| | - Millard H. Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, United States
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34
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Tkáč O, Rusher CA, Greaves SJ, Orr-Ewing AJ, Dagdigian PJ. Differential and integral cross sections for the rotationally inelastic scattering of methyl radicals with H2and D2. J Chem Phys 2014; 140:204318. [DOI: 10.1063/1.4879618] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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35
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Tkáč O, Orr-Ewing AJ, Dagdigian PJ, Alexander MH, Onvlee J, van der Avoird A. Collision dynamics of symmetric top molecules: a comparison of the rotationally inelastic scattering of CD3 and ND3 with He. J Chem Phys 2014; 140:134308. [PMID: 24712794 DOI: 10.1063/1.4869596] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We compare rotationally inelastic scattering of deuterated methyl radicals (CD3) and ammonia (ND3) in collisions with helium using close-coupling quantum-mechanical scattering calculations performed with ab initio potential energy surfaces (PESs). The theoretical methods have been rigorously tested against angle-resolved experimental measurements obtained using crossed molecular beam apparatuses in combination with velocity map imaging [O. Tkáč, A. G. Sage, S. J. Greaves, A. J. Orr-Ewing, P. J. Dagdigian, Q. Ma, and M. H. Alexander, Chem. Sci. 4, 4199 (2013); O. Tkáč, A. K. Saha, J. Onvlee, C.-H. Yang, G. Sarma, C. K. Bishwakarma, S. Y. T. van de Meerakker, A. van der Avoird, D. H. Parker, and A. J. Orr-Ewing, Phys. Chem. Chem. Phys. 16, 477 (2014)]. Common features of the scattering dynamics of these two symmetric top molecules, one closed-shell and the other an open-shell radical, are identified and discussed. Two types of anisotropies in the PES influence the interaction of an atom with a nonlinear polyatomic molecule. The effects of these anisotropies can be clearly seen in the state-to-state integral cross sections out of the lowest CD3 rotational levels of each nuclear spin symmetry at a collision energy of 440 cm(-1). Similarities and differences in the differential cross sections for the ND3-He and CD3-He systems can be linked to the coupling terms derived from the PESs which govern particular initial to final rotational level transitions.
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Affiliation(s)
- Ondřej Tkáč
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Andrew J Orr-Ewing
- School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom
| | - Paul J Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, USA
| | - Millard H Alexander
- Department of Chemistry and Biochemistry and Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742-2021, USA
| | - Jolijn Onvlee
- Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525AJ Nijmegen, The Netherlands
| | - Ad van der Avoird
- Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525AJ Nijmegen, The Netherlands
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36
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Chen J, Dagdigian PJ. Radiative and Nonradiative Decay of Electronically Excited HNF and DNF. Isr J Chem 2013. [DOI: 10.1002/ijch.199400006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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37
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Melchior A, Mark Lambert H, Dagdigian PJ, Bar I, Rosenwaks S. The Photodissociation of Ground and Vibrationally Excited Halogenated Alkanes. Isr J Chem 2013. [DOI: 10.1002/ijch.199700051] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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38
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Dagdigian PJ, Alexander MH. Exact quantum scattering calculations of transport properties for the H2O–H system. J Chem Phys 2013; 139:194309. [DOI: 10.1063/1.4829681] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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39
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McGurk SJ, McKendrick KG, Costen ML, Alexander MH, Dagdigian PJ. Parity-dependent oscillations in collisional polarization transfer: CN(A²Π, v = 4) + Ar. J Chem Phys 2013; 139:124304. [PMID: 24089764 DOI: 10.1063/1.4821602] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We report the first systematic experimental and theoretical study of the state-to-state transfer of rotational angular momentum orientation in a (2)Π-rare gas system. CN(X(2)Σ(+)) was produced by pulsed 266 nm photolysis of ICN in a thermal bath (296 K) of Ar collider gas. A pulsed circularly polarized tunable dye laser prepared CN(A(2)Π, v = 4) in two fully state-selected initial levels, j = 6.5 F1e and j = 10.5 F2f, with a known laboratory-frame orientation. Both the prepared levels and a range of product levels, j' F1e and j' F2f, were monitored using the circular polarized output of a tunable diode laser via cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM Doppler lineshapes for co-rotating and counter-rotating pump-and-probe geometries reveal the time-dependence of the populations and orientations. Kinetic fitting was used to extract the state-to-state population transfer rate constants and orientation multipole transfer efficiencies (MTEs), which quantify the degree of conservation of initially prepared orientation in the product level. Complementary full quantum scattering (QS) calculations were carried out on recently computed ab initio potential energy surfaces. Collision-energy-dependent tensor cross sections for ranks K = 0 and 1 were computed for transitions from both initial levels to all final levels. These quantities were integrated over the thermal collision energy distribution to yield predictions of the experimentally observed state-to-state population transfer rate constants and MTEs. Excellent agreement between experiment and theory is observed for both measured quantities. Dramatic oscillations in the MTEs are observed, up to and including changes in the sign of the orientation, as a function of even/odd Δj within a particular spin-orbit and e/f manifold. These oscillations, along with those also observed in the state-to-state rate constants, reflect the rotational parity of the final level. In general, parity-conserving collisions conserve rotational orientation, while parity-changing collisions result in large changes in the orientation. The QS calculations show that the dynamics of the collisions leading to these different outcomes are fundamentally different. We propose that the origin of this behavior lies in interferences between collisions that sample the even and odd-λ terms in the angular expansions of the PESs.
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Affiliation(s)
- S J McGurk
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
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40
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Lehman JH, Lester MI, Kłos J, Alexander MH, Dagdigian PJ, Herráez-Aguilar D, Aoiz FJ, Brouard M, Chadwick H, Perkins T, Seamons SA. Electronic Quenching of OH A 2Σ+ Induced by Collisions with Kr Atoms. J Phys Chem A 2013; 117:13481-90. [DOI: 10.1021/jp407035p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Julia H. Lehman
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | - Marsha I. Lester
- Department
of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323, United States
| | | | | | - Paul J. Dagdigian
- Department
of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218-2685, United States
| | - Diego Herráez-Aguilar
- Departamento
de Quimica Fisica, Facultad de Quimica, Universidad Complutense, Madrid 28040, Spain
| | - F. Javier Aoiz
- Departamento
de Quimica Fisica, Facultad de Quimica, Universidad Complutense, Madrid 28040, Spain
| | - Mark Brouard
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Helen Chadwick
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Tom Perkins
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - Scott A. Seamons
- The Physical
and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom
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41
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42
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Lique F, Werfelli G, Halvick P, Stoecklin T, Faure A, Wiesenfeld L, Dagdigian PJ. Spin-orbit quenching of the C+(2P) ion by collisions with para- and ortho-H2. J Chem Phys 2013; 138:204314. [PMID: 23742482 DOI: 10.1063/1.4807311] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Spin-orbit (de-)excitation of C(+)((2)P) by collisions with H2, a key process for astrochemistry, is investigated. Quantum-mechanical calculations of collisions between C(+) ions and para- and ortho-H2 have been performed in order to determine the cross section for the C(+) (2)P3∕2 → (2)P1∕2 fine-structure transition at low and intermediate energies. The calculation are based on new ab initio potential energy surfaces obtained using the multireference configuration interaction method. Corresponding rate coefficients were obtained for temperatures ranging from 5 to 500 K. These rate coefficients are compared to previous estimations, and their impact is assessed through radiative transfer computation. They are found to increase the flux of the (2)P3∕2 → (2)P1∕2 line at 158 μm by up to 30% for typical diffuse interstellar cloud conditions.
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Affiliation(s)
- François Lique
- LOMC - UMR 6294, CNRS-Université du Havre, 25, Rue Philippe Lebon, BP 540, 76058 Le Havre, France.
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43
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Dagdigian PJ, Alexander MH. Exact quantum scattering calculations of transport properties: CH2(X̃3B1, ã1A1)–helium. J Chem Phys 2013; 138:164305. [DOI: 10.1063/1.4801789] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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44
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Dagdigian PJ, Alexander MH. Theoretical study of the vibrational relaxation of the methyl radical in collisions with helium. J Chem Phys 2013; 138:104317. [DOI: 10.1063/1.4794167] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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45
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Tkáč O, Sage AG, Greaves SJ, Orr-Ewing AJ, Dagdigian PJ, Ma Q, Alexander MH. Rotationally inelastic scattering of CD3 and CH3 with He: comparison of velocity map-imaging data with quantum scattering calculations. Chem Sci 2013. [DOI: 10.1039/c3sc52002a] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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46
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Dagdigian PJ, Alexander MH. Exact quantum scattering calculation of transport properties for free radicals: OH(X2Π)–helium. J Chem Phys 2012; 137:094306. [DOI: 10.1063/1.4748141] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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47
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Gubbels KB, Ma Q, Alexander MH, Dagdigian PJ, Tanis D, Groenenboom GC, van der Avoird A, van de Meerakker SYT. Resonances in rotationally inelastic scattering of OH(X2Π) with helium and neon. J Chem Phys 2012; 136:144308. [PMID: 22502519 DOI: 10.1063/1.3697816] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present detailed calculations on resonances in rotationally and spin-orbit inelastic scattering of OH (X(2)Π, j = 3/2, F(1), f) radicals with He and Ne atoms. We calculate new ab initio potential energy surfaces for OH-He, and the cross sections derived from these surfaces compare well with the recent crossed beam scattering experiment of Kirste et al. [Phys. Rev. A 82, 042717 (2010)]. We identify both shape and Feshbach resonances in the integral and differential state-to-state scattering cross sections, and we discuss the prospects for experimentally observing scattering resonances using Stark decelerated beams of OH radicals.
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Affiliation(s)
- Koos B Gubbels
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany.
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48
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Dagdigian PJ, Alexander MH. Theoretical investigation of rotationally inelastic collisions of CH2(X̃) with helium. J Chem Phys 2012; 136:224306. [DOI: 10.1063/1.4729050] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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49
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McGurk SJ, McKendrick KG, Costen ML, Bennett DIG, Kłos J, Alexander MH, Dagdigian PJ. Depolarization of rotational angular momentum in CN(A2Π, v = 4) + Ar collisions. J Chem Phys 2012; 136:164306. [PMID: 22559481 DOI: 10.1063/1.4705118] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Angular momentum depolarization and population transfer in CN(A(2)Π, v = 4, j, F(1)e) + Ar collisions have been investigated both experimentally and theoretically. Ground-state CN(X(2)Σ(+)) molecules were generated by pulsed 266-nm laser photolysis of ICN in a thermal (nominally 298 K) bath of the Ar collision partner at a range of pressures. The translationally thermalized CN(X) radicals were optically pumped to selected unique CN(A(2)Π, v = 4, j = 2.5, 3.5, 6.5, 11.5, 13.5, and 18.5, F(1)e) levels on the A-X (4,0) band by a pulsed tunable dye laser. The prepared level was monitored in a collinear geometry by cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM lineshapes for co- and counter-rotating circular pump and probe polarizations were analyzed to extract the time dependence of the population and (to a good approximation) orientation (tensor rank K = 1 polarization). The corresponding parallel and perpendicular linear polarizations yielded population and alignment (K = 2). The combined population and polarization measurements at each Ar pressure were fitted to a 3-level kinetic model, the minimum complexity necessary to reproduce the qualitative features of the data. Rate constants were extracted for the total loss of population and of elastic depolarization of ranks K = 1 and 2. Elastic depolarization is concluded to be a relatively minor process in this system. Complementary full quantum scattering (QS) calculations were carried out on the best previous and a new set of ab initio potential energy surfaces for CN(A)-Ar. Collision-energy-dependent elastic tensor and depolarization cross sections for ranks K = 1 and 2 were computed for CN(A(2)Π, v = 4, j = 1.5-10.5, F(1)e) rotational/fine-structure levels. In addition, integral cross sections for rotationally inelastic transitions out of these levels were computed and summed to yield total population transfer cross sections. These quantities were integrated over a thermal collision-energy distribution to yield the corresponding rate constants. A complete master-equation simulation using the QS results for the selected initial level j = 6.5 gave close, but not perfect, agreement with the near-exponential experimental population decays, and successfully reproduced the observed multimodal character of the polarization decays. On average, the QS population removal rate constants were consistently 10%-15% higher than those derived from the 3-level fit to the experimental data. The QS and experimental depolarization rate constants agree within the experimental uncertainties at low j, but the QS predictions decline more rapidly with j than the observations. In addition to providing a sensitive test of the achievable level of agreement between state-of-the art experiment and theory, these results highlight the importance of multiple collisions in contributing to phenomenological depolarization using any method sensitive to both polarized and unpolarized molecules in the observed level.
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Affiliation(s)
- S J McGurk
- School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom
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Dagdigian PJ. EXPERIMENTAL STUDIES OF ROTATIONALLY INELASTIC STATE-RESOLVED COLLISIONS OF SMALL MOLECULAR FREE RADICALS. ACTA ACUST UNITED AC 2012. [DOI: 10.1142/9789814317184_0008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/07/2023]
Affiliation(s)
- Paul J. Dagdigian
- Department of Chemistry, The Johns Hopkins University, Baltimore, MD 21218, USA
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