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

Comparisons are presented of experimental and theoretical studies of the rotationally inelastic scattering of CD{sub 3} radicals with H{sub 2} and D{sub 2} collision partners at respective collision energies of 680 ± 75 and 640 ± 60 cm{sup −1}. Close-coupling quantum-mechanical calculations performed using a newly constructed ab initio potential energy surface (PES) provide initial-to-final CD{sub 3} 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 CD{sub 3} scattering from both H{sub 2} and D{sub 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 CD{sub 3} n → n′ transition have a similar angular dependence with either D{sub 2} or H{sub 2} as collision partner. Any differences between DCSs or ICSs can be attributed to mass effects because the PES is unchanged for CD{sub 3}−H{sub 2} and CD{sub 3}–D{sub 2} collisions. Further comparisons are drawn between the CD{sub 3}–D{sub 2} scattering and results for CD{sub 3}–He presented in our recent paper [O. Tkáč, 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.