Elastic and inelastic differential cross-sections for the scattering of Xe(³P₂,₀) by CH₃I at superthermal collision energies

Differential cross-sections for the elastic scattering of Xe(3 P 2,0) atoms by CH3I have been determined at the following collision energies: 32·2, 48·5, 68·6, 92·5, 120·2 kJ mol-1. The elastic scattering is heavily depleted at all scattering angles and an optical model analysis is used to derive differential and integral cross-sections for the competing inelastic channels from the optimized opacity functions. In the Xe(3 P 2,0)/CH3I system, where the inelastic channel is almost exclusively excitation transfer, the differential scattering is largely in the forward hemisphere and there is no evidence for any steric constraint. This contrasts with the analogous system Cs/CH3I where the inelastic channel is reactive and the collision dynamics follow the ‘rebound’ model. On the other hand, the excitation functions for both atom and excitation transfer in Xe(3 P 2,0)/CH3I follow the same collision energy dependence (σ(E CM) ∝ E CM -0·5) implying passage over an orbiting barrier which precedes the branching into alternative channels.