Vacuum ultraviolet photodissociation dynamics of isocyanic acid: the hydrogen elimination channel.

Photodissociation dynamics of the H-atom channel from HNCO photolysis between 124 and 137 nm have been studied using the H-atom Rydberg tagging time-of-flight technique. Product translational energy distributions and angular distributions have been determined. Two dissociation channels, H + NCO (X(2)Π) and H + NCO(A(2)Σ(+)), have been observed. The former channel involves two different dissociation pathways; one is a slow predissociation pathway through internal conversion from the excited state to the S0 state, and the other is a fast predissociation pathway through internal conversion from the excited state to the S1 state. The latter channel dominates by a prompt dissociation via coupling to the S2 state. As the photon energy increases, dissociation on the ground state S0 becomes dominant. Vibrational structures are observed in both the NCO(X) and NCO(A) channels, which can be assigned to the bending mode excitation with some stretching vibrational excitation.