  When a chemical reaction is driven by an external field, the transition state
that the system must pass through as it changes from reactant to product -for
example, an energy barrier- becomes time-dependent. We show that for periodic
forcing the rate of barrier crossing can be determined through stability
analysis of the non-autonomous transition state. Specifically, strong agreement
is observed between the difference in the Floquet exponents describing
stability of the transition state trajectory, which defines a recrossing-free
dividing surface [G. T. Craven, T. Bartsch, and R. Hernandez, Phys. Rev. E 89,
040801(R) (2014)], and the rates calculated by simulation of ensembles of
trajectories. This result opens the possibility to extract rates directly from
the intrinsic stability of the transition state, even when it is
time-dependent, without requiring a numerically-expensive simulation of the
long-time dynamics of a large ensemble of trajectories.
