BRANCHING RATIO FOR THE H+NCO CHANNEL IN THE 193 NM PHOTODISSOCIATIONOF HNCO

The H atom quantum yield phi(H) and the average product translational energy were determined for the HNCO --> H(S-2) + NCO(X(2)II) photodiss ociation channel at room temperature for a photolysis wavelength of 19 3 nm. HNCO was photolyzed using an ArF excimer laser and nascent H ato ms were detected by vacuum-UV-laser-induced fluorescence at the Lyman- alpha transition. With a calibration method using HCl photolysis as a source of well-defined H atom concentrations, a value of phi(H) = 0.20 +/- 0.04 for the H atom quantum yield was measured. From H atom Doppl er profiles, measured under single collision conditions, the fraction f(T) of the available energy released as product translational energy was determined to be f(T)(H + NCO)= 0.69 +/- 0.09.