Dynamic Coupling Phenomena in Molecular Excited States. II. Autoionization and Predissociation inH2, Hd, andD2

Abstract
Vibrationally induced autoionization and one class of predissociation of electronically excited H2 and its isotopes are treated by a perturbed-stationary-state theory. Autoionization and predissociation rates are given for a number of states of H2, HD, and D2. In addition to direct bound-continuum coupling, consideration is given to effects of higher-order coupling; these effects cause order-of-magnitude changes in isolated cases. The auto-ionization rates vary with principal quantum number n as n3, directly with vibrational energy vhν, and decrease sharply with vibrational quantum change Δv. As the principal quantum number increases, transitions of successively smaller Δv become possible; the net effect of this is to override the n3 dependence in total autoionization rates. Competition between predissociation and autoionization is examined; the two processes show very different dependence on n and v, with the consequence that decay in most regions of (n, v) space is dominated by one or the other process; but the two mechanisms are competitive for some (n, v) states. The isotope effect also is rather different for the two decay processes, enough so that, in effect, the isotope effect amounts to a qualitative change from one mechanism of decay to the other, with mass change.