A New (Cartesian) Reaction-path Model for Dynamics in Polyatomic Systems, with Application to H-atom Transfer in Malonaldehyde

A new kind of reaction-path model for describing reactions in polyatomic molecular systems is presented, based on the Cartesian coordinates of the atoms. Not only does this lead to a simpler treatment of the interaction between the ‘system ’ ( i e. the reaction coordinate) and the ‘bath ’ (the other degrees of freedom) than earlier reaction-path models based on the (curvi-linear) steepest-descent reaction path, but in many cases it also provides a more natural description of the dynamics. The resulting Hamiltonian has the standard form of a Cartesian ‘system ’ linearly coupled to a harmonic ‘bath’, the dynamics of which is treated in this paper by the basis set method of Makri and Miller (J. Chem. Phys., 1987,86, 1451). Application to a model of H-atom transfer in malonaldehyde shows that the overall approach (both the Cartesian reaction-path model and the basis-set method treatment of the dynamics) is quite successful. 1