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Abstract
Quantum scattering calculations on collisional rotational and vibrational energy transfer in small hydrocarbon reactive intermediates are highlighted. This review focuses on recent theoretical studies of energy transfer in methylene (CH2), in both its ground triplet
3
B
1 and low-lying singlet
1
A
1 electronic states, and in the methyl (CH3) radical. Propensities in the state-to-state cross sections are shown to depend upon the two types of anisotropies that are present in potential energy surfaces of systems involving nonlinear polyatomic molecules. Computed rate constants for rotational and vibrational relaxation are compared with available experimental data. In addition, collisional transfer between the CH2
and
states is addressed. Collision-induced intersystem crossing is shown to be mediated by spectroscopically perturbed rotational levels of mixed electronic character.
Acknowledgements
The author is very grateful for the support of Millard Alexander, with whom he has collaborated for many years on studies of the dynamics of molecular collisions and for encouraging the author to undertake scattering calculations. This article represents a review of our joint effort on collisional energy transfer in polyatomic intermediates. The author also warmly acknowledges Lifang Ma at the University of Maryland and Qianli Ma at The Johns Hopkins University, who carried out much of the work described in this review. He is also appreciative of Gregory Hall and Trevor Sears at Brookhaven National Laboratory for sharing data from their recent experiments on the collisional relaxation of (
) and for their encouragement. This work was supported by the Chemical, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, under Grant No. DESC0002323.