Spin-orbit branching in the predissociation of the C1Π in state of HCl and DCl:: A manifestation of quantum interference

We report a combined theoretical-experimental investigation of the predissociation of HCl subsequent to photoexcitation of the lowest Rydberg state of (1)Pi symmetry (C (1)Pi). Our particular interest is the characterization of the configurational mixing between this state and the lower, repulsive valence state of (1)Pi symmetry (A (1)Pi). A plausible model for the coupling between these two states, which also involves spin-orbit coupling between the C state and the a (3)Pi(1) and t (3)Sigma(1)(+) states, leads to predicted spin-orbit branching ratios, for both HCl and DCl, which agree qualitatively with the results of a new experimental investigation, also reported here. The theoretical simulation further strongly suggests that the observed predissociation branching ratios reflect quantum interference effects. (C) 1998 Elsevier Science B.V. All rights reserved.