  The framework of transition state theory relies on the determination of a
geometric structure identifying reactivity. It replaces the laborious exercise
of following many trajectories for a long time to provide chemical reaction
rates and pathways. In this paper, recent advances in constructing this
geometry even in time-dependent systems are applied to the LiCN
$\rightleftharpoons$ LiNC isomerization reaction, driven by an external field.
We obtain decay rates of the reactant population close to the transition state
by exploiting local properties of the dynamics of trajectories in and close to
it. We find that the external driving has a large influence on these decay
rates when compared to the non-driven isomerization reaction. This, in turn,
provides renewed evidence for the possibility of controlling chemical
reactions, like this one, through external time-dependent fields.
