Photodissociation dynamics of HNCO at 248 nm

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+hv-->H(S-2)+NCO(X(2)II) were detected by vacuum-UV laser-induced fluorescence (VUY-LIF) at the Lyman-alpha transition. By means of a calibration method - using H2S photolysis as a source of well defined H atom concentrations - the absolute cross section for direct photolytic H atom formation was determined to be sigma(H)=(1.2+/-0.3)x10(-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+hv-->NH(X (3) Sigma(-))+CO(X(1) Sigma(+)), was investigated. Our results show that at a wavelength of 248 nm, direct Il atom formation is the dominant dissociation channel in the HNCO photolysis.