Gas phase photofragmentation dynamics of HNCO/DNCO after laser excitation at 222 nM

Using the laser photolysis/laser-induced fluorescence (LP/LIF) pump-probe t echnique, the gas phase photofragmentation dynamics of HNCO and DNCO at roo m temperature was studied at photolysis wavelength of 222 nm. H/D atoms pro duced via HNCO/DNCO (X(1)A) + h nu --> H/D(S-2) + NCO ((XP)-P-2) were detec ted by (2p(2)P --> 1s(2)S) LIF. The quantum yield for photofragmentation in to H atom channel has been measured to be phi(H)(222 nm) = (0.33+/-0.04) fo r HNCO. For the isotopomer DNCO the quantum yield value was phi(D)(222 nm)= (0.4+/-0.09). From H/D atom Doppler profiles measured under single collisi on conditions, the fraction f(T), of the available energy released as produ ct translational energy was determined to be f(T) (H+NCO) =(0.37+/-0.03) an d f(T) (D+NCO) =(0.36+/-0.03) at 222 nm. The experimental results suggest t hat isomerisation from the optically excited trans HNCO to cis HNCO followe d by dissociation on S-1 surface is the prevalent mechanism at this wavelen gth.