The Doppler profiles of the hydrogen atom photofragments from the photodissociation of HCl and HBr at 157 and 243 nm are observed to determine the symmetries of the photoexcited states by using a resonance enhanced multiphoton ionization technique. The phototransitions are perpendicular for HCl at 157 nm and 193 nm and for HBr at 157 nm and 243 nm. Isotope effects on the branching ratios of lsqb;Clast;(2P1/2)rsqb;/lsqb;Cl(2P3/2)rsqb; are observed for the photodissociation of HCl and DCl at 157 and 193 nm. Our results indicate that in the photodissociation processes of HCl (Athinsp;1Pgr;) the dynamical curve crossings during the breakup of the molecule play important roles in the determination of the branching ratio.
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