This is the peer-reviewed author's version of a work that was accepted for publication in Chemical Physics Letters. Changes resulting from the publishing process, such as editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version

(1999) 'A failing of coupled-states calculations for inelastic and pressure-broadening cross sections : calculations on CO2Ar.', Journal of chemical physics., 111 (13). pp. 5824-5828. Further information on publisher's website: http://dx. The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full DRO policy for further details. Close coupling calculations for rotational relaxation of CO in argon: Accuracy of energy corrected sudden scaling procedures and comparison with experimental data Comparison of an ab initio calculation of the CO-Ar P(2) line shape with high-resolution measurements AIP Conf. Energy corrected sudden calculations of line widths and line shapes based on coupled states cross sections: The test case of CO 2-argon AIP Conf. Fully quantal benchmark calculations of pressure-broadening cross sections for infrared and Raman lines of CO 2 perturbed by Ar are carried out using both close-coupling CC and coupled-states CS calculations. CS calculations are found to underestimate the cross sections by up to 15%. The effect occurs even for isotropic Raman cross sections, which are not affected by reorientation contributions. The discrepancy arises mostly for collisions with large orbital angular momenta l, occurring on the long-range part of the potential. It may be attributed to collisions that are adiabatic rather than sudden in nature. A hybrid computational method, employing CS calculations for low l and decoupled l-dominant DLD calculations for high l, offers a promising solution.

Rate constants for collisional loss and transfer of population and rotational angular momentum alignment have been determined for the CN(A 2 Π, v = 4) + Ar system. Aligned samples of CN(A 2 Π, v = 4, F 1 , j = 1.5 -23.5 e) were prepared by optical pumping on the A-X(4,0) band. Their evolution was observed using Doppler-resolved Frequency-Modulated Spectroscopy in stimulated emission on the A-X(4,2) band. Stateresolved total population removal rate constants, and state-to-state rotational energy transfer (RET) rate constants, are found to be in excellent agreement with previous experimental measurements and theoretical predictions for the v = 3 level. Rapid elastic depolarization of rotational alignment was observed for j = 1.5 -6.5, with an average rate constant of 1.1 x 10 -10 cm 3 s -1. This declines with increasing j, reaching zero within experimental error for j = 23.5. The polarization transfer efficiency of the initially created alignment in state-to-state RET was also determined for the selected initial state j = 6.5, F 1 , e. Substantial depolarization of the alignment was observed for small ∆j transitions. Alignment transfer efficiencies ranged from 0.55 ± 0.06 for ∆j = -1, to 0.32 ± 0.08 for ∆j = +3. These measurements are discussed with reference to recent experimental and theoretical advances on collisional depolarization of related open-shell species. We suggest that the surprisingly efficient collisional depolarization observed may be the result of the multiple potential energy surfaces involved in this system.

Polarized laser photolysis of ICN is combined with saturated optical pumping to prepare state-selected CN Alpha(2)Pi (nu' = 4, J = 0.5, F(2), f) with a well-defined anisotropic superthermal speed distribution. The collisional evolution of the prepared state is observed by Doppler-resolved Frequency Modulated (FM) spectroscopy via stimulated emission on the CN Alpha(2)Pi-Chi(2)Sigma(+) (4,2) band. The phenomenological rate constants for removal of the prepared state in collisions with He, Ar, N(2) and O(2) are reported. The observed collision cross-sections are consistent with attractive forces contributing significantly for all the colliders with the exception of He. The collisional evolution of the prepared velocity distribution demonstrates that no significant back-transfer into the prepared level occurs, and that any elastic scattering is strongly in the forward hemisphere.