Branching ratio for the H + NCO channel in the 193 nm photodissociation of HNCO

The H atom quantum yield ΦH and the average product translational energy were determined for the HNCO→ H(2S) + NCO(X2Π) photodissociation channel at room temperature for a photolysis wavelength of 193 nm. HNCO was photolyzed using an ArF excimer laser and nascent H atoms were detected by vacuum-UV-laser-induced fluorescence at the Lyman-α transition. With a calibration method using HCl photolysis as a source of well-defined H atom concentrations, a value of ΦH = 0.20 ± 0.04 for the H atom quantum yield was measured. From H atom Doppler profiles, measured under single collision conditions, the fraction fT of the available energy released as product translational energy was determined to be fT(H + NCO) = 0.69 ± 0.09.