Quantum scattering studies of electronically inelastic collisions of CN (X 2Σ+, A 2Π) with He

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Abstract
Using recent ab initio interaction potential energy surfaces for the CN (X 2Σ+, A 2Π)+He system [H.‐J. Werner, B. Follmeg, and M. H. Alexander, J. Chem. Phys. 8 9, 3139 (1988)], we have calculated fully quantum cross sections for inelastic transitions between individual rovibrational levels of the A 2Π and the X 2Σ+ states of CN. We have concentrated on the transitions studied experimentally by Dagdigian and co‐workers for CN+Ar, namely transitions between the rotational levels of the A, v=8 and X, v’=12, the A, v=7 and X, v’=11, and the A, v=3 and X, v’=7 vibrational manifolds. In the case of the 8→12 and 7→11 transitions the cross sections are large (0.1–1 Å2), and the dependence on initial Λ doublet level and on final rotational quantum number displays the same subtle alternations as seen experimentally. In the case of the 3→7 transitions, for which the vibrational levels are energetically much more separated, the calculated cross sections for CN+He are extremely small (10−5 Å2), far smaller than observed experimentally for CN+Ar. In order to resolve this discrepancy, we have carried out some additional ab initio calculations for the CN+Ar system, but the change in the interelectronic coupling potential appears not to be large enough to explain the magnitude of the experimental cross sections.

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