Theoretical study of bifurcating reaction paths

Abstract

Theoretical study has been given on bifurcating reaction paths where the intrinsic reaction path (IRP) has a valley-ridge inflection (VRI) point on the way from transition state to product, and leads to another first-order saddle point which connects two symmetrically equivalent products. To extract dynamically important regions in the configuration space between the VRI point and products, a group of steepest descent paths are calculated starting from zero-point energy regions at the VRI point, and the obtained configuration space is analyzed in terms of the reaction coordinate and the normal coordinate. The method is applied to Berry pseudorotations in SiH4F− and PH4F, H3CO→H2COH, and cyclopropylidene→allene, by employing the second-order Mo/ller–Plesset and complete active space self-consistent field ab initio molecular orbital calculations. It is shown that the extension of bifurcating reaction paths largely depends on the position of the VRI point on the IRP. For the respective reactions, non-totally symmetric excited states are calculated along the IRP to understand the valley-ridge inflection mechanism in terms of the second-order Jahn–Teller effect. The isotope effect on bifurcating reaction paths is also investigated.