title: Competition between direct and indirect dissociation pathways in ultraviolet photodissociation of HNCO.
abstract: Photodissociation dynamics of HNCO at photolysis wavelengths between 200 and 240 nm have been studied using the H-atom Rydberg tagging time-of-flight technique. Product translational energy distributions and angular distributions have been determined. At low photon energy excitation, the product translational energy distribution is nearly statistical and the angular distribution is isotropic, which is consistent with an indirect dissociation mechanism, i.e., internal conversion from S1 to S0 surface and dissociation on S0 surface. As the photon energy increases, a direct dissociation pathway on S1 surface opens up. The product translational energy distribution appears to be quite nonstatistical and the product angular distribution is anisotropic. The fraction of direct dissociation pathway is determined to be 36 ± 5% at 202.67 nm photolysis. Vibrational structures are observed in both direct and indirect dissociation pathways, which can be assigned to the NCO bending mode excitation with some stretching excitation.
authors.affiliation: State key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , 457 Zhongshan Road, Dalian 116023, China.
authors.forename: Shengrui
authors.initials: S
authors.lastname: Yu
authors.forename: Shu
authors.initials: S
authors.lastname: Su
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Dorenkamp
authors.forename: Alec M
authors.initials: AM
authors.lastname: Wodtke
authors.forename: Dongxu
authors.initials: D
authors.lastname: Dai
authors.forename: Kaijun
authors.initials: K
authors.lastname: Yuan
authors.forename: Xueming
authors.initials: X
authors.lastname: Yang
mesh_terms: D003485:Cyanates / Q000737:chemistry*; D055668:Photochemical Processes; D010782:Photolysis; D011789:Quantum Theory; D013499:Surface Properties; D014466:Ultraviolet Rays
chemical_list: D003485:Cyanates; C005057:isocyanic acid