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Lehmann KK. Polarization-dependent intensity ratios in double resonance spectroscopy. J Chem Phys 2023; 159:184202. [PMID: 37937939 DOI: 10.1063/5.0172828] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 09/29/2023] [Indexed: 11/09/2023] Open
Abstract
Double Resonance is a powerful spectroscopic method that unambiguously assigns the rigorous quantum numbers of one state of a transition. However, there is often ambiguity as to the branch (ΔJ) of that transition. Spectroscopists have resolved this ambiguity by using the dependence of the double resonance intensity on the relative polarization directions of pump and probe radiation. However, published theoretical predictions for this ratio are based upon a weak (i.e., non-saturating) field approximation. This paper presents theoretical predictions for these intensity ratios for cases where the pump field is strongly saturating in the two limits of transitions dominated by homogeneous or of inhomogeneous broadening. Saturation reduces but does not eliminate the magnitude of the polarization effect (driving the intensity ratio closer to unity) even with strong pump saturation. For the case of an inhomogeneously broadened line, such as when Doppler broadened linewidth dominates over the power-broadened homogeneous line width, a large fraction of the low pump power polarization anisotropy remains. This paper reports predicted polarization ratios for both linear and circular pump and probe field polarizations. The present predictions are compared with experimental measurements on CH4 ground state → ν3 → 3ν3 transitions recently reported by de Oliveira et al.63 and these are in better agreement than with the weak field predictions.
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Affiliation(s)
- Kevin K Lehmann
- Departments of Chemistry and Physics, University of Virginia, Charlottesville, Virginia 22904-4319, USA
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Egorov O, Rey M, Nikitin AV, Viglaska D. New Theoretical Infrared Line List for the Methyl Radical with Accurate Vibrational Band Origins from High-Level Ab Initio Calculations. J Phys Chem A 2022; 126:6429-6442. [PMID: 36073030 DOI: 10.1021/acs.jpca.2c04822] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In the present work, high-level ab initio calculations were carried out for the ground electronic state of the methyl radical (CH3). Dunning's augmented correlation-consistent orbital basis sets were employed up to the quintuple-ζ valence quality with the core-valence electron correlation [aug-cc-pCV5Z] combined with the single- and double-excitation unrestricted coupled-cluster approach with a perturbative treatment of triple excitations [RHF-UCCSD(T)]. The explicitly correlated version of the coupled-cluster approach [RHF-UCCSD(T)-F12x{x = a, b}] was additionally applied with the core-valence cc-pCVQZ-F12 basis set in order to study convergence with respect to the basis set size. The contributions beyond the coupled-cluster level of the theory like Douglas-Kroll-Hess scalar relativistic Hamiltonian, diabatic Born-Oppenheimer corrections, and high-order electronic correlations have been included into the ab initio potential energy surfaces (PESs). It is shown that the theoretical band origins of CH3 converge gradually to the experimental values when applying the ab initio PESs using the aug-cc-pCVXZ [X = T, Q, and 5] basis sets. For the first time, all available experimental band origins of the gaseous CH3 are reproduced within an accuracy of 0.2 cm-1 using a newly developed PES extrapolated to the complete basis set limit [CBS(TQ5Z)]. The reached accuracy is one order of magnitude better than that of the best available calculations. A new theoretical infrared line list was generated for astrophysical applications using an ab initio dipole moment surface computed at the RHF-UCCSD(T)/aug-cc-pCVQZ level of the theory. The manifestation of a large-amplitude motion in CH3 is also discussed.
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Affiliation(s)
- Oleg Egorov
- Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics SB RAS 1, Akademician Zuev Sq., Tomsk 634055 Russia
| | - Michaël Rey
- Groupe de Spectrométrie Moléculaire et Atmosphérique UMR CNRS 7331, UFR Sciences BP 1039, 51687 Reims Cedex 2, France
| | - Andrei V Nikitin
- Laboratory of Theoretical Spectroscopy, V.E. Zuev Institute of Atmospheric Optics SB RAS 1, Akademician Zuev Sq., Tomsk 634055 Russia
| | - Dominika Viglaska
- Groupe de Spectrométrie Moléculaire et Atmosphérique UMR CNRS 7331, UFR Sciences BP 1039, 51687 Reims Cedex 2, France
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Loos PF, Scemama A, Boggio-Pasqua M, Jacquemin D. Mountaineering Strategy to Excited States: Highly Accurate Energies and Benchmarks for Exotic Molecules and Radicals. J Chem Theory Comput 2020; 16:3720-3736. [DOI: 10.1021/acs.jctc.0c00227] [Citation(s) in RCA: 37] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Affiliation(s)
- Pierre-François Loos
- Laboratoire de Chimie et Physique Quantiques, CNRS, UPS, Université de Toulouse, 31000 Toulouse, France
| | - Anthony Scemama
- Laboratoire de Chimie et Physique Quantiques, CNRS, UPS, Université de Toulouse, 31000 Toulouse, France
| | - Martial Boggio-Pasqua
- Laboratoire de Chimie et Physique Quantiques, CNRS, UPS, Université de Toulouse, 31000 Toulouse, France
| | - Denis Jacquemin
- CEISAM UMR 6230, CNRS, Université de Nantes, F-44000 Nantes, France
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Adam AY, Yachmenev A, Yurchenko SN, Jensen P. Variationally Computed IR Line List for the Methyl Radical CH 3. J Phys Chem A 2019; 123:4755-4763. [PMID: 31050423 DOI: 10.1021/acs.jpca.9b02919] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We present the first variational calculation of a hot-temperature ab initio line list for the CH3 radical. It is based on a high-level ab initio potential energy surface and dipole moment surface of CH3 in the ground electronic state. The ro-vibrational energy levels and Einstein A coefficients were calculated using the general-molecule variational approach implemented in the computer program TROVE. Vibrational energies and vibrational intensities are found to be in very good agreement with the available experimental data. The line list comprises 9 127 123 ro-vibrational states ( J ≤ 40) and 2 058 655 166 transitions, covering the wavenumber range up to 10 000 cm-1 and should be suitable for temperatures up to T = 1500 K.
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Affiliation(s)
- Ahmad Y Adam
- Fakultät für Mathematik und Naturwissenschaften, Physikalische und Theoretische Chemie , Bergische Universität Wuppertal , D-42097 Wuppertal , Germany
| | - Andrey Yachmenev
- Center for Free-Electron Laser Science , Deutsches Elektronen-Synchrotron DESY , Notkestraβe 85 , D-22607 Hamburg , Germany.,The Hamburg Center for Ultrafast Imaging , Universität Hamburg , Luruper Chaussee 149 , D-22761 Hamburg , Germany
| | - Sergei N Yurchenko
- Department of Physics and Astronomy , University College London , Gower Street , WC1E 6BT London , U.K
| | - Per Jensen
- Fakultät für Mathematik und Naturwissenschaften, Physikalische und Theoretische Chemie , Bergische Universität Wuppertal , D-42097 Wuppertal , Germany
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Zanchet A, Bañares L, Senent ML, García-Vela A. An ab initio study of the ground and excited electronic states of the methyl radical. Phys Chem Chem Phys 2018; 18:33195-33203. [PMID: 27892569 DOI: 10.1039/c6cp05960k] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The ground and some excited electronic states of the methyl radical have been characterized by means of highly correlated ab intio techniques. The specific excited states investigated are those involved in the dissociation of the radical, namely the 3s and 3pz Rydberg states, and the A1 and B1 valence states crossing them, respectively. The C-H dissociative coordinate and the HCH bending angle were considered in order to generate the first two-dimensional ab initio representation of the potential surfaces of the above electronic states of CH3, along with the nonadiabatic couplings between them. Spectroscopic constants and frequencies calculated for the ground and bound excited states agree well with most of the available experimental data. Implications of the shape of the excited potential surfaces and couplings for the dissociation pathways of CH3 are discussed in the light of recent experimental results for dissociation from low-lying vibrational states of CH3. Based on the ab initio data some predictions are made regarding methyl photodissociation from higher initial vibrational states.
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Affiliation(s)
- A Zanchet
- Instituto de Física Fundamental, CSIC, C/Serrano, 123, 28006 Madrid, Spain.
| | - L Bañares
- Departamento de Química Física I, Facultad de Ciencias Químicas, Universidad Complutense de Madrid (Unidad Asociada I+D+i CSIC), 28040 Madrid, Spain
| | - M L Senent
- Departamento de Química y Física Teóricas, Instituto de Estructura de la Materia, CSIC, C/Serrano, 121, 28006 Madrid, Spain
| | - A García-Vela
- Instituto de Física Fundamental, CSIC, C/Serrano, 123, 28006 Madrid, Spain.
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Blitz MA, Green NJB, Shannon RJ, Pilling MJ, Seakins PW, Western CM, Robertson SH. Reanalysis of Rate Data for the Reaction CH3 + CH3 → C2H6 Using Revised Cross Sections and a Linearized Second-Order Master Equation. J Phys Chem A 2015; 119:7668-82. [DOI: 10.1021/acs.jpca.5b01002] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. A. Blitz
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - N. J. B. Green
- Inorganic
Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QR, U.K
| | - R. J. Shannon
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - M. J. Pilling
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - P. W. Seakins
- School
of Chemistry, University of Leeds, Leeds LS2 9JT, U.K
| | - C. M. Western
- School
of Chemistry, Cantock’s Close, Bristol BS8 1TS, U.K
| | - S. H. Robertson
- Dassault Systèmes, BIOVIA, Science Park, Cambridge CB4 0WN, U.K
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Ram NB, Krishnakumar E. Dissociative electron attachment to methane probed using velocity slice imaging. Chem Phys Lett 2011. [DOI: 10.1016/j.cplett.2011.05.065] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Costen ML, McKendrick KG. Orientation and alignment moments in two-color polarization spectroscopy. J Chem Phys 2005; 122:164309. [PMID: 15945686 DOI: 10.1063/1.1883646] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
A theoretical analysis of two-color polarization spectroscopy (TCPS) is presented as an extension of a previous analysis of one-color PS. Three commonly used schemes in which pump and probe transitions share a common level are considered. Diagrammatic techniques are used to isolate the photon interaction sequences that can contribute to the signal. A perturbation-theory analysis expressing the signal in terms of spherical tensor moments is applied. The analysis emphasises the significance of orientation and alignment tensor moments of rotational angular momentum and their collisional evolution. The assumed context is transitions between single rotational states of gas-phase molecules that subsequently suffer discrete collisions. The time scale of the measurements is assumed to be long relative to the periods of molecular motion, as would typically be the case for signals excited by nanosecond-pulsed lasers from samples at moderate pressures. The Doppler motion of the probed species is included, as is an analytical solution to the integration over the Maxwell-Boltzmann distribution of velocities. The effects of nuclear hyperfine depolarization and velocity-changing collisions are discussed. It is shown that when pump- and probe-laser pulses are separated in time, TCPS creates and probes either orientation or alignment of rotational angular momentum in the common level shared by pump and probe transitions. Example simulations of one- and two-color polarization spectroscopies are included to demonstrate the resulting simplification of the measured signal using TCPS. TCPS is therefore a viable spectroscopic technique for the determination of rotational angular momentum orientation and alignment relaxation rates in molecular gases, of interest because they are sensitive probes of inelastic collisions.
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Affiliation(s)
- Matthew L Costen
- School of Engineering and Physical Sciences, William H. Perkin Building, Heriot-Watt University, Edinburgh, EH14 4AS United Kingdom.
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