Reaction-path dynamics with harmonic vibration frequencies in curvilinear internal coordinates: H+trans-N2H2→N2H+H 2

This paper presents a general method for treating doubly degenerate bending vibrations of bonds with 180 deg bond angles in curvilinear coordinates along a reaction path. The new treatment improves the generalized normal mode frequencies needed for rate constant calculations with variational transition state theory and for multidimensional semiclassical tunneling calculations. We apply this method to calculate harmonic vibrational frequencies and rate constants for the reaction $\mathrm{H}+\mathit{trans}-{\mathrm{N}}_{\mathrm{2}}{\mathrm{H}}_{\mathrm{2}}{\mathrm{\to N}}_{\mathrm{2}}{\mathrm{H+H}}_{\mathrm{2}}.$ The new results are compared to earlier calculations employing rectilinear Cartesian coordinates in order to evaluate the sensitivity of the calculations to the coordinate system chosen.