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Chang Z, Satija A, Lucht RP. Two-color polarization spectroscopy measurements of Zeeman state-to-state collision induced transitions of nitric oxide in binary gas mixtures. J Chem Phys 2023; 159:244309. [PMID: 38153153 DOI: 10.1063/5.0177626] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2023] [Accepted: 12/05/2023] [Indexed: 12/29/2023] Open
Abstract
We investigated collision induced transitions in the (0, 0) band of the A2Σ+-X2Π electronic transition of nitric oxide (NO) using two-color polarization spectroscopy (TCPS). Two sets of TCPS spectra for 1% NO, diluted in different buffer gases at 295 K and 1 atm, were obtained with the pump beam tuned to the R11(11.5) and OP12(1.5) transitions. The buffer gases were He, Ar, and N2. The probe was scanned while the pump beam was tuned to the line center. Theoretical TCPS spectra, calculated by solving the density matrix formulation of the time-dependent Schrödinger wave equation, were compared with the experimental spectra. A collision model based on the modified exponential-gap law was used to model the rotational level-to-rotational level collision dynamics. A model for collisional transfer from an initial to a final Zeeman state was developed based on the difference in cosine of the rotational quantum number J projection angle with the z-axis for the two Zeeman states. Rotational energy transfer rates and Zeeman state collisional dynamics were varied to obtain good agreement between theory and experiment for the two different TCPS pump transitions and for the three different buffer gases. One key finding, in agreement with quasi-classical trajectory calculations, is that the spin-rotation changing transition rate in the A2Σ+ level of NO is almost zero for rotational quantum numbers ≥8. It was necessary to set this rate to near zero to obtain agreement with the TCPS spectra.
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Affiliation(s)
- Ziqiao Chang
- School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Aman Satija
- School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA
| | - Robert P Lucht
- School of Mechanical Engineering, Purdue University, West Lafayette, Indiana 47907, USA
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2
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Nautiyal VV, Devi S, Tyagi A, Vidhani B, Maan A, Prasad V. Orientation and Alignment dynamics of polar molecule driven by shaped laser pulses. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2021; 256:119663. [PMID: 33827039 DOI: 10.1016/j.saa.2021.119663] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Revised: 02/17/2021] [Accepted: 02/28/2021] [Indexed: 06/12/2023]
Abstract
We review the theoretical status of intense laser induced orientation and alignment-a field of study which lies at the interface of intense laser physics and chemical dynamics and having potential applications such as high harmonic generation, nano-scale processing and control of chemical reactions. The evolution of the rotational wave packet and its dynamics leading to orientation and alignment is the topic of the present discussion. The major part of this article primarily presents an overview of recent theoretical progress in controlling the orientation and alignment dynamics of a molecule by means of shaped laser pulses. The various theoretical approaches that lead to orientation and alignment such as static electrostatic field in combination with laser field(s), combination of orienting and aligning field, combination of aligning fields, combination of orienting fields, application of train of pulses etc. are discussed. It is observed that the train of pulses is quite an efficient tool for increasing the orientation or alignment of a molecule without causing the molecule to ionize. The orientation and alignment both can occur in adiabatic and non-adiabatic conditions with the rotational period of the molecule taken under consideration. The discussion is mostly limited to non-adiabatic rotational excitation (NAREX) i.e. cases in which the pulse duration is shorter than the rotational period of the molecule. We have emphasised on the so called half-cycle pulse (HCP) and square pulse (SQP). The effect of ramped pulses and of collision on the various laser parameters is also studied. We summarize the current discussion by presenting a consistent theoretical approach for describing the action of such pulses on movement of molecules. The impact of a particular pulse shape on the post-pulse dynamics is also calculated and analysed. In addition to this, the roles played by various laser parameters including the laser frequency, the pulse duration and the system temperature etc. are illustrated and discussed. The concept of alignment is extended from one-dimensional alignment to three-dimensional alignment with the proper choice of molecule and the polarised light. We conclude the article by discussing the potential applications of intense laser orientation and alignment.
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Affiliation(s)
- Vijit V Nautiyal
- Department of Physics and Astrophysics, University of Delhi, Delhi, Delhi 110007, India
| | - Sumana Devi
- Department of Physics and Astrophysics, University of Delhi, Delhi, Delhi 110007, India; Department of Physics, Miranda House College, University of Delhi, Delhi, Delhi 110007, India
| | - Ashish Tyagi
- Department of Physics, Swami Shradhanand College, University of Delhi, Delhi, Delhi 110036, India
| | - Bhavna Vidhani
- Department of Physics, Hansraj College, University of Delhi, Delhi, Delhi 110007, India
| | - Anjali Maan
- Department of Physics, Pt.N.R.S.G.C.Rohtak, Maharshi Dayanand University, Rohtak 124001, Haryana, India
| | - Vinod Prasad
- Department of Physics, Swami Shradhanand College, University of Delhi, Delhi, Delhi 110036, India.
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3
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Hammami H, Ben Mohamed F, Mohamed D, Ben El Hadj Rhouma M, Al Mogren MM, Hochlaf M. One-electron pseudo-potential investigation of NO(X 2Π)–Ar n clusters ( n = 1,2,3,4). Mol Phys 2017. [DOI: 10.1080/00268976.2017.1337252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- H. Hammami
- Laboratoire de Recherche d'Etude des Milieux Ionisés et Réactifs (EMIR), Institut Préparatoire aux Etudes d'Ingénieurs, Université de Monastir, Tunisie
| | - F.E. Ben Mohamed
- Laboratoire de Recherche d'Etude des Milieux Ionisés et Réactifs (EMIR), Institut Préparatoire aux Etudes d'Ingénieurs, Université de Monastir, Tunisie
| | - D. Mohamed
- Laboratoire de Recherche d'Etude des Milieux Ionisés et Réactifs (EMIR), Institut Préparatoire aux Etudes d'Ingénieurs, Université de Monastir, Tunisie
| | - M. Ben El Hadj Rhouma
- Laboratoire de Recherche d'Etude des Milieux Ionisés et Réactifs (EMIR), Institut Préparatoire aux Etudes d'Ingénieurs, Université de Monastir, Tunisie
| | - M. M. Al Mogren
- Chemistry Department, Faculty of Science, King Saud University, Riyadh, Kingdom of Saudi Arabia
| | - M. Hochlaf
- Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, Université Paris-Est, Marne-la-Vallée, France
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4
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Holmes-Ross HL, Valenti RJ, Yu HG, Hall GE, Lawrance WD. Rotational and angular distributions of NO products from NO-Rg (Rg = He, Ne, Ar) complex photodissociation. J Chem Phys 2016; 144:044309. [PMID: 26827219 DOI: 10.1063/1.4940690] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We present the results of an investigation into the rotational and angular distributions of the NO à state fragment following photodissociation of the NO-He, NO-Ne, and NO-Ar van der Waals complexes excited via the à ← X̃ transition. For each complex, the dissociation is probed for several values of Ea, the available energy above the dissociation threshold. For NO-He, the Ea values probed were 59, 172, and 273 cm(-1); for NO-Ne they were 50 and 166 cm(-1); and for NO-Ar they were 44, 94, 194, and 423 cm(-1). The NO à state rotational distributions arising from NO-He are cold, with most products in low angular momentum states. NO-Ne leads to broader NO rotational distributions but they do not extend to the maximum possible given the energy available. In the case of NO-Ar, the distributions extend to the maximum allowed at that energy and show the unusual shapes associated with the rotational rainbow effect reported in previous studies. This is the only complex for which a rotational rainbow effect is observed at the chosen Ea values. Product angular distributions have also been measured for the NO à photodissociation product for the three complexes. NO-He produces nearly isotropic fragments, but the anisotropy parameter, β, for NO-Ne and NO-Ar photofragments shows a surprising change in sign from negative to positive as Ea increases within the unstructured excitation profile. Franck-Condon selection of a broader distribution of geometries including more linear geometries at lower excitation energies and more T-shaped geometries at higher energies can account for the changing recoil anisotropy. Two-dimensional wavepacket calculations are reported to model the rotational state distributions and the bound-continuum absorption spectra.
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Affiliation(s)
- Heather L Holmes-Ross
- School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia
| | - Rebecca J Valenti
- School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia
| | - Hua-Gen Yu
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
| | - Gregory E Hall
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973-5000, USA
| | - Warren D Lawrance
- School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, Adelaide, South Australia 5001, Australia
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5
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Zhang X, Eyles CJ, Ding D, Stolte S. The modified quasi-quantum treatment of rotationally inelastic NO(X)-He scattering. Phys Chem Chem Phys 2015; 17:4067-75. [PMID: 25589218 DOI: 10.1039/c4cp01733a] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
A modified quasi-quantum treatment (MQQT) of molecular scattering has been developed to account for the softness of the repulsive part of the anisotropic atom-molecule PES. A contour of the PES is chosen such that the barrier height is just large enough to reflect the incoming kinetic energy, directed anti-parallel to the hard shell normal at the site of impact. The resulting rotationally inelastic quantum state resolved DCSs and ICSs of He + NO(X) at Ecol = 508 cm(-1) are compared to those obtained from regular QQT and from quantum mechanically exact calculations performed on the full highest quality ab initio Vsum PES. The MQQT parity changing DCSs for Δj ≤ 4 exhibit much better agreement with the QM DCSs than is obtained using regular QQT, particularly in the forward scattered direction. The improvements upon the remaining MQQT DCSs with respect to the regular QQT were minor, due to the near incompressible hard shell character of the n ≠ 1 or 3 anisotropic Legendre polynomial terms of the PES.
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Affiliation(s)
- Xia Zhang
- Institute of Atomic and Molecular Physics, Jilin University, Changchun, 130012, China.
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Tkáč O, Ma Q, Stei M, Orr-Ewing AJ, Dagdigian PJ. Rotationally inelastic scattering of methyl radicals with Ar and N2. J Chem Phys 2015; 142:014306. [PMID: 25573560 DOI: 10.1063/1.4904901] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
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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Brouard M, Chadwick H, Gordon SDS, Hornung B, Nichols B, Kłos J, Aoiz FJ, Stolte S. Fully quantum state-resolved inelastic scattering of NO(X) + Kr: Differential cross sections and product rotational alignment. J Chem Phys 2014; 141:164306. [DOI: 10.1063/1.4897558] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- M. Brouard
- The Department of Chemistry, University of Oxford, The Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - H. Chadwick
- The Department of Chemistry, University of Oxford, The Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - S. D. S. Gordon
- The Department of Chemistry, University of Oxford, The Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - B. Hornung
- The Department of Chemistry, University of Oxford, The Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - B. Nichols
- The Department of Chemistry, University of Oxford, The Physical and Theoretical Chemistry Laboratory, South Parks Road, Oxford OX1 3QZ, United Kingdom
| | - J. Kłos
- Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA
| | - F. J. Aoiz
- Departamento de Química Física, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain
| | - S. Stolte
- Institute of Atomic and Molecular Physics, Jilin University, Changchun 130012, China
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Niane A, Dath CAB, Faye NAB, Hammami K, Jaidane NE. Rotationally inelastic dynamics of LiH (X(1)Σ(+), v = 0) in collisions with Ar: State-to-state inelastic rotational rate coefficients. SPRINGERPLUS 2014; 3:188. [PMID: 24808997 PMCID: PMC4012032 DOI: 10.1186/2193-1801-3-188] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 02/26/2014] [Indexed: 11/10/2022]
Abstract
A theoretical study of rotational collision of LiH(X(1)Σ(+),v = 0, J) with Ar has been carried out. The ab initio potential energy surface (PES) describing the interaction between the Ar atom and the rotating LiH molecule has been calculated very accurately and already discussed in our previous work [Computational and Theoretical Chemistry 993 (2012) 20-25]. This PES is employed to evaluate the de-excitation cross sections. The ab initio PES for the LiH(X(1)Σ(+))-Ar((1)S) Van der waals system is calculated at the coupled-cluster [CCSD(T)] approximation for a LiH length fixed to an experimental value of 3.0139 bohrs. The basis set superposition error (BSSE) is corrected and the bond functions are placed at mid-distance between the center of mass of LiH and the Ar atom. The cross sections are then derived in the close coupling (CC) approach and rate coefficients are inferred by averaging these cross sections over a Maxwell-Boltzmann distribution of kinetic energies. The 11 first rotational levels of rate coefficients are evaluated for temperatures ranging from 10 to 300 K. We notice that the de-excitation rate coefficients appear large in the order 10(-10) cm(-3) s(-1) and show very low temperature dependence. The rate coefficients magnify significantly the propensity toward ∆ J = -1 transitions. These results confirm the same propensity already noted for the cross sections.
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Affiliation(s)
- Aliou Niane
- Laboratory of Atoms Lasers, Department of Physics, Faculty of Science and Techniques, University Cheikh Anta Diop of Dakar, Dakar, Senegal
| | - Cheikh Amadou Bamba Dath
- Laboratory of Atoms Lasers, Department of Physics, Faculty of Science and Techniques, University Cheikh Anta Diop of Dakar, Dakar, Senegal
| | - Ndèye Arame Boye Faye
- Laboratory of Atoms Lasers, Department of Physics, Faculty of Science and Techniques, University Cheikh Anta Diop of Dakar, Dakar, Senegal
| | - Kamel Hammami
- Laboratory for Atomic Molecular Spectroscopy and Applications, Department of Physics, Faculty of Science, University Tunis El Manar, Campus Universities, 1060 Tunis, Tunisia
| | - Nejm-Eddine Jaidane
- Laboratory for Atomic Molecular Spectroscopy and Applications, Department of Physics, Faculty of Science, University Tunis El Manar, Campus Universities, 1060 Tunis, Tunisia
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9
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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] [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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10
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Brouard M, Chadwick H, Eyles CJ, Hornung B, Nichols B, Scott JM, Aoiz FJ, Kłos J, Stolte S, Zhang X. The fully quantum state-resolved inelastic scattering of NO(X) + Ne: experiment and theory. Mol Phys 2013. [DOI: 10.1080/00268976.2013.783940] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Affiliation(s)
- M. Brouard
- a Department of Chemistry, The Physical and Theoretical Chemistry Laboratory , University of Oxford , Oxford , United Kingdom
| | - H. Chadwick
- a Department of Chemistry, The Physical and Theoretical Chemistry Laboratory , University of Oxford , Oxford , United Kingdom
| | - C. J. Eyles
- a Department of Chemistry, The Physical and Theoretical Chemistry Laboratory , University of Oxford , Oxford , United Kingdom
| | - B. Hornung
- a Department of Chemistry, The Physical and Theoretical Chemistry Laboratory , University of Oxford , Oxford , United Kingdom
| | - B. Nichols
- a Department of Chemistry, The Physical and Theoretical Chemistry Laboratory , University of Oxford , Oxford , United Kingdom
| | - J. M. Scott
- a Department of Chemistry, The Physical and Theoretical Chemistry Laboratory , University of Oxford , Oxford , United Kingdom
| | - F. J. Aoiz
- b Departamento de Química Física, Facultad de Química , Universidad Complutense , Madrid , Spain
| | - J. Kłos
- c Department of Chemistry and Biochemistry , University of Maryland , College Park , MD , USA
| | - S. Stolte
- d Atomic and Molecular Physics Institute , Jilin University , Changchun , China
- e Laser Center , Vrije Universiteit , Amsterdam , The Netherlands
- f Laboratoire Francis Perrin , Bâtiment 522, DRECEM/SPAM/CEA Saclay, Gif sur Yvette , France
| | - X. Zhang
- d Atomic and Molecular Physics Institute , Jilin University , Changchun , China
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Zhang X, Eyles CJ, Taatjes CA, Ding D, Stolte S. A general scaling rule for the collision energy dependence of a rotationally inelastic differential cross-section and its application to NO(X) + He. Phys Chem Chem Phys 2013; 15:5620-35. [PMID: 23471220 DOI: 10.1039/c3cp50558h] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The quasi-quantum treatment (QQT) (Gijsbertsen et al., J. Am. Chem. Soc., 2006, 128, 8777) provides a physically compelling framework for the evaluation of rotationally inelastic scattering, including the differential cross sections (DCS). In this work the QQT framework is extended to treat the DCS in the classically forbidden region as well as the classically allowed region. Most importantly, the QQT is applied to the collision energy dependence of the angular distributions of these DCSs. This leads to an analytical formalism that reveals a scaling relationship between the DCS calculated at a particular collision energy and the DCS at other collision energies. This scaling is shown to be exact for QM calculated or experimental DCSs if the magnitude of the (kinematic apse frame) underlying scattering amplitude depends solely on the projection of the incoming momentum vector onto the kinematic apse vector. The QM DCSs of the NO(X)-He collision system were found to obey this scaling law nearly perfectly for energies above 63 meV. The mathematical derivation is accompanied by a mechanistic description of the Feynman paths that contribute to the scattering amplitude in the classically allowed and forbidden regions, and the nature of the momentum transfer during the collision process. This scaling relationship highlights the nature of (and limits to) the information that is obtainable from the collision-energy dependence of the DCS, and allows a description of the relevant angular range of the DCSs that embodies this information.
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Affiliation(s)
- Xia Zhang
- Institute of Atomic and Molecular Physics, Jilin University, Changchun, 130012, China
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12
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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] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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13
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Jambrina PG, Kłos J, Aoiz FJ, de Miranda MP. New findings regarding the NO angular momentum orientation in Ar-NO(2Π(1/2)) collisions. Phys Chem Chem Phys 2012; 14:9826-37. [PMID: 22710404 DOI: 10.1039/c2cp41043e] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
This article reports a theoretical study of the stereodynamics of Ar + NO(X(2)Π, v = 0, j = 1/2, Ω = 1/2, ε = ±1) rotationally inelastic collisions. First, quantum scattering data are used to calculate all differential polarisation moments of the reagent and product molecules; this leads to the observation that the orientations of the reagent and product angular momenta are very strongly correlated. Next, canonical collision mechanisms theory [Aldegunde et al., Phys. Chem. Chem. Phys., 2008, 10, 1139] is used to separate and characterise the stereodynamics of the two independent collision mechanisms that contribute to the collision dynamics; this leads to the observation that the average product orientation is determined by the relative contributions of the two canonical mechanisms, which have comparable importance but are associated with starkly contrasting angular momentum orientations. These observations lead to a new and rigorous explanation of the experimental results reported a decade ago by Lorenz et al. [Science, 2001, 293, 2063]. The central fact of the new explanation is the incoherent, interference-free superposition of two independent collision mechanisms. This makes the new explanation radically different from the only one previously suggested, namely that the experimental observations might be due to quantum interference in a single collision mechanism.
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Affiliation(s)
- Pablo G Jambrina
- Departamento de Química Física, Facultad de Ciencias Químicas, Universidad de Salamanca, 37008 Salamanca, Spain
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14
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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] [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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Paterson G, Costen ML, McKendrick KG. Collisional depolarisation of rotational angular momentum: influence of the potential energy surface on the collision dynamics? INT REV PHYS CHEM 2012. [DOI: 10.1080/0144235x.2012.659046] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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