Least-Action Tunneling Transmission Coefficient for Polyatomic Reactions

We present a new least-action variational approximation for tunneling in polyatomic reactions based on the procedure developed by Garrett and Truhlar for atom-diatom reactions. (63) The method calculates the semiclassical ground-state tunneling probability at every tunneling energy by minimizing the value of imaginary action integral along a family of paths ranging from the minimum energy path to the straight path. The method is illustrated by applications to two hydrogen-atom abstraction reactions from methane using analytical potential energy surfaces.