Photodissociation dynamics of HNCO at 248 nm

• Published in: Chemical physics letters 1996-08, Vol.258 (1), p.164-170
• Main Authors: Brownsword, R.A., Laurent, T., Vatsa, R.K., Volpp, H.-R., Wolfrum, J.
• Format: Article
• Language: English
• ISSN: 0009-2614; 1873-4448
• DOI: 10.1016/0009-2614(96)00626-4

Using the laser photolysis/laser-induced fluorescence (LP/LIF) pump-probe technique, the gas-phase photodissociation dynamics of room temperature HNCO was studied at a photolysis wavelength of 248 nm. H atoms produced via HNCO + hν → H( 2 S) + NCO( X 2Π) were detected by vacuum-UV laser-induced fluorescence (VUV-LIF) at the Lyman-α transition. By means of a calibration method — using H 2S photolysis as a source of well defined H atom concentrations — the absolute cross section for direct photolytic H atom formation was determined to be σ H = (1.2 ± 0.3) × 10 −21 cm 2 molecule −1. From the H atom Doppler profiles, measured under single-collision conditions, the fraction of the available energy released as product translational energy was determined to be f T(H + NCO) = (0.55 ± 0.02). In addition, the second energetically accessible ‘spin-forbidden’ dissociation channel, HNCO + hν → NH( X 3Σ −) + CO( X 1Σ +) , was investigated. Our results show that at a wavelength of 248 nm, direct H atom formation is the dominant dissociation channel in the HNCO photolysis.