Subdiffusion supports barrier crossing: Mittag-Leffler noise autocorrelation and reactive flux formalism as evidence

Rate constants govern the overcoming of potential energy barriers in chemical reactions. In the simplest approach, quasi-equilibrium in the presence of a white noise bath is advocated as the triggering mechanism. Heat baths can be tricky; around the barrier, they can retain memory, which entails non-white noise. The generalised Langevin equation is here used as the underlying model with a noise term whose autocorrelation is described by a Mittag-Leffler function of one, two, or three parameters. In the framework of reactive flux formalism, the rate constant is calculated directly as a function of the barrier height, the friction coefficient, and the parameters of the employed Mittag-Leffler function. In the strong damping limit, because of the generality of the approach, it becomes clear that noises that lead to subdiffusion promote barrier crossing as opposed to those that support superdiffusion.