Reaction-path dynamics in curvilinear internal coordinates including torsions

We describe a procedure for calculating generalized normal mode vibrational frequencies along a reaction path in curvilinear coordinates for a polyatomic system involving torsions. We apply the method to calculate generalized normal mode frequencies and rate constants for the OH+H2→H2O+H reaction using variational transition state theory with a multidimensional semiclassical tunneling approximation for the transmission coefficient. The results are compared to rate calculations carried out in rectilinear Cartesian coordinates to test the sensitivity of the calculated thermal rate constants to the choice of coordinate.