  The spin-dependent Berry force is a genuine effect of Berry curvature in
molecular dynamics, which can dramatically result in spatial spin separation
and change of reaction pathways. However, the way to probe the effect of Berry
force remains challenging, because the time-reversal (TR) symmetry required for
opposite Berry forces conflicts with TR symmetry breaking spin alignment needed
to observe the effect, and the net effect could be transient for a molecular
wave packet. We demonstrate that in molecular photodissociation, the
dissociation rates can be different for molecules with opposite initial spin
directions due to Berry force. We showcase that the spatially separated spin
density, which is transiently induced by Berry force as the molecular wave
packet passes through conical intersection, can be reconstructed from the
circular dichroism (CD) of ultrafast non-resonant magnetic x-ray scattering
using free electron lasers.
