  We investigate how the Berry force (i.e. the pseudo-magnetic force operating
on nuclei as induced by electronic degeneracy and spin-orbit coupling (SOC))
might modify a post-transition state bifurcation (PTSB) reaction path and
affect product selectivity for situations when multiple products share the same
transition state. To estimate the magnitude of this effect, Langevin dynamics
are performed on a model system with a valley-ridge inflection (VRI) point in
the presence of a magnetic field (that mimics the Berry curvature). We also
develop an analytic model for such selectivity that depends on key parameters
such as the surface topology, the magnitude of the Berry force, and the nuclear
friction. Within this dynamical model, static electronic structure calculations
(at the level of generalized Hartree-Fock with spin-orbit coupling (GHF+SOC)
theory) suggest that electronic-spin induced Berry force effects may indeed
lead to noticeable changes in methoxy radical isomerization.
