Spin-forbidden dehydrogenation of methoxy cation: a statistical view

A non-adiabatic version of RRKM theory is applied to predicting the microca nonical rates for different mechanisms of spin-forbidden dissociation of me thoxy cation and its isotopically substituted derivatives, to formyl cation and dihydrogen. The predictions are in agreement with experimental results on this system, and in particular with the occurrence of a "direct" mechan ism for dissociation, rather than of an indirect one cin hydroxyethyl catio n. Ab initio computations were used throughout to provide the parameters ne eded to apply the non-adiabatic RRKM theory, and the success of this strate gy is shown to be promising for other applications in polyatomic systems. F inally, the kinetic energy release distribution for loss of hydrogen from m ethoxy and hydroxymethyl cations are computed using ab initio "direct dynam ics" classical trajectories at the HF/6-31G** level, their similarity is al so in agreement with experiment.