Photodissociation of hydrogen chloride at 157 and 193 nm: Angular distributions of hydrogen atoms and fine-structure branching ratios of chlorine atoms in the 2Pj levels.

The H, D, and Cl atoms from the photodissociation of HCl and DCl at 157 and 193 nm were detected by laser-induced fluorescence (LIF) in the vacuum ultraviolet region. The Doppler profiles of the H and D resonance lines at 121.6 nm in the LIF spectra indicate that the absorption of HCl and DCl at 157 nm is a mixture of perpendicular and parallel transition (A 1Π, a 3Π0+←X 1Σ+), while that at 193 nm results almost solely from the A 1Π←X 1Σ+ transition. The fine-structure branching ratios, are measured for the chlorine atom by LIF. Combined with the previous results, the branching ratios [Cl*(2P1/2)]/[Cl(2P3/2)] are 0.81±0.09 at 157 nm, 0.50±0.05 at 193 nm for HCl, and 0.23±0.05 at 193 nm for DCl. These results suggest that the nonadiabatic couplings during the breakup of HCl (DCl) in the excited states play an important role in determination of the fine-structure branching ratios. [ABSTRACT FROM AUTHOR]