Translational energy dependence of the Cl + CH4(v b = 0, 1) reactions: a joint crossed-beam and quasiclassical trajectory study

Abstract

The Cl + CH4(v b = 0, 1) reactions were studied over a wide range of collision energies, from threshold up to 20 kcal mol−1, using joint experimental and theoretical methods. Experiments were performed under crossed-beam conditions using a time-sliced velocity imaging detection method. Both the pair-correlated integral and differential cross sections were measured. Theoretically, quasiclassical trajectory calculations were performed on a highly accurate ab initio potential energy surface. The computed results show very good agreement with experimental findings. The underlying reaction mechanisms are as below: the formation of HCl(v′ = 0) products is mainly governed by direct scatterings, whereas the HCl(v′ = 1) channel is mediated by a time-delayed mechanism, likely invoking reactive resonances. In addition, the spin-orbit excited Cl*(2 P 1/2) reactivity was experimentally characterized. The results compare favourably with a recently reported reduced dimensionality quantum dynamics calculation, and with the previous reports on the isotopically analogous reactions. Possible involvement of resonances in this spin-orbit nonadiabatic process is suggested and awaits further investigations.