A semiclassical model for tunneling from one classically allowed region on a potential
energy surface to another is described. The principal feature of this model, compared to
earlier (more ''rigorous'') multidimensional semiclassical tunneling theories, is that it can be
implemented in a straightforward way within the framework of a standard classical trajectory
simulation. Applications to several examples of unimolecular isomerization and
unimolecular dissociation show that the model is capable of providing excellent results over …