Improving reduced dimensionality quantum reaction dynamics with a generalized transition state. Application to CH4+O(P-3)

We present a new procedure to calculate rate constants from reduced dimensi onality reaction probabilities. The method combines an energy-shifting corr ection, as used in reduced dimensionality calculations of three and four-at om reactions, with a generalized transition state. The procedure, in combin ation with a recently developed reduced dimensionality model, is used to ca lculate rate constants for CH4+O(P-3)--> CH3+OH and its fully deuterated co unterpart. These rate constants are compared with the ones obtained using t he standard technique and with experimental values. Also, we study the effe ct on reactivity of exciting selected modes of methane. Similarities and di fferences between the deuterated and undeuterated reactions are discussed. (C) 2001 American Institute of Physics.