Ultraviolet photodissociation of HCl in selected rovibrational states: Experiment and theory

Experimental and theoretical methods have been applied to investigate the e ffect of internal parent excitation on the ultraviolet photodissociation dy namics of HCl (X (1)Sigma(+)) molecules. Jet-cooled (HCl)-Cl-35 molecules w ithin a time-of-flight mass spectrometer were prepared by infra-red absorpt ion in the following quantum states: upsilon = 1, J = 0 and J = 5; upsilon = 2, J = 0 and J = 11; upsilon = 3, J = 0 and J = 7. The excited molecules were then photodissociated at lambda similar to 235 nm and the Cl(P-2(j)) p hotofragments detected using (2 + 1) resonance enhanced multiphoton ionizat ion. The results are presented as the fraction of total chlorine yield form ed in the spin-orbit excited state, Cl(P-2(1/2)). The experimental measurem ents are compared with the theoretical predictions from a time-dependent, q uantum dynamical treatment of the photodissociation dynamics of HCl (upsilo n = 1-3, J = 0). These calculations involved wavepacket propagation using t he ab initio potential energy curves and coupling elements previously repor ted by Alexander, Pouilly, and Duhoo [J. Chem. Phys. 99, 1752 (1993)]. The experimental results and theoretical predictions share a common qualitative trend, although quantitative agreement occurs only for HCl (upsilon = 2). (C) 2000 American Institute of Physics. [S0021-9606(00)00923-5].