The multiplet state distribution of O(3PJ) produced in the photodissociation of O2 at 157 nm

The fine structure population of O(³P) produced in the photodissociation of O₂ at 157 nm was measured in a pump-and-probe experiment. The population of the ground state (J=2) was found to be 93%, with only 6% in the J=1 level and 1% in J=0. The predominance of J=2 is consistent with direct dissociation on the B ³Σ^-_u potential energy surface. Based on available information in the literature we rule out excitation of the ³Π_u state and curve crossing to the ⁵Π_u state as possible origins of the population with J<2. We infer that the populations of J<2 is due to nonadiabatic transitions at large distances. Two mechanisms consistent with the data are a Demkov-type interaction, which is caused by coupling by the radial kinetic energy operator.