Statistical and nonstatistical nonadiabatic photodissociation from the first excited state of the hydroxymethyl radical.

Photodissociation of hydroxymethyl (H(2)COD) from the first excited state, a Rydberg 3s state, can produce either H+HCOD or H(2)CO+D. These processes involve a seam of conical intersections. An analysis of the seam is reported based on a pointwise determination of the three gradient vectors that characterize a conical intersection: the energy difference gradient and the coupling gradient, which span the branching space, and the gradient of the average energy. These data are used to understand why H, but not D is produced at energies near threshold, the difference in the recoil anisotropy for H and D dissociation, and whether H or D will be produced impulsively or after formation of an intermediate complex.