Differential and integral cross sections for the rotationally inelastic scattering of methyl radicals with H-2 and D-2

Comparisons are presented of experimental and theoretical studies of the rotationally inelastic scattering of CD3 radicals with H-2 and D-2 collision partners at respective collision energies of 680 +/- 75 and 640 +/- 60 cm(-1). Close-coupling quantum-mechanical calculations performed using a newly constructed ab initio potential energy surface (PES) provide initial-to-final CD3 rotational level (n, k -> n', k') integral and differential cross sections (ICSs and DCSs). The DCSs are compared with crossed molecular beam and velocity map imaging measurements of angular scattering distributions, which serve as a critical test of the accuracy of the new PES. In general, there is very good agreement between the experimental measurements and the calculations. The DCSs for CD3 scattering from both H-2 and D-2 peak in the forward hemisphere for n' = 2-4 and shift more to sideways and backward scattering for n' = 5. For n' = 6-8, the DCSs are dominated by backward scattering. DCSs for a particular CD3 n -> n' transition have a similar angular dependence with either D-2 or H-2 as collision partner. Any differences between DCSs or ICSs can be attributed to mass effects because the PES is unchanged for CD3-H-2 and CD3-D-2 collisions. Further comparisons are drawn between the CD3-D-2 scattering and results for CD3-He presented in our recent paper [O. Tkac, A. G. Sage, S. J. Greaves, A. J. Orr-Ewing, P. J. Dagdigian, Q. Ma, and M. H. Alexander, Chem. Sci. 4, 4199 (2013)]. These systems have the same reduced mass, but are governed by different PESs. (C) 2014 AIP Publishing LLC.