where k TST is expressed in Eq. 197, and κ Q is the corresponding transmission coefficient. This transmission coefficient κ Q = κ ZPE • κ S has two components, a zero-point energy (ZPE) correction (contributing to enthalpy) to the transmission coefficient κ ZPE , and an entropic component κ S that depends on the normal mode frequencies of reactant and the stable normal mode frequencies at the transition state configuration. Under the high temperature limit, κ S ≈ κ GH , and the κ Q ≈ κ GH (with κ ZPE ≈ 1). Under the low temperature limit, κ Q ≈ κ ZPE .