  We investigate the nuclear dynamics near a real-valued conical intersection
that is perturbed by a complex-valued spin-orbit coupling. For a model
Hamiltonian with two outgoing channels, we find that even a small spin-orbit
coupling can dramatically affect the pathway selection on account of Berry
force, leading to extremely large spin selectivity (sometime as large as 100%).
Thus, this Letter opens the door for organic chemists to start designing
spintronic devices that use nuclear motion and conical intersections (combined
with standard spin-orbit coupling) in order to achieve spin selection. Vice
versa, for physical chemists, this Letter also emphasizes that future
semiclassical simulations of intersystem crossing (which have heretofore
ignored Berry force) should be corrected to account for the spin polarization
that inevitably arises when dynamics pass near conical intersections.
