LINE-SHAPES AND DECAY DYNAMICS OF DISSOCIATIVE RESONANCES ABOVE THE 2ND DISSOCIATION LIMIT OF MOLECULAR-HYDROGEN

We have systematically studied the line shapes and dynamics of several dissociative resonances near the second dissociation limits of H-2, D -2, and HD. Spectral overlap is eliminated using laser double resonanc e through the EF (1) Sigma(g)(+) state, and state-selective detection is used to distinguish dissociation to the H(1s) + H(2s) and H(1s)+ H( 2p) channels. The threshold region contains both dissociative Rydberg states belonging to the 3p complex and shape resonances from the B, B' , and C states. Line shapes range from nearly symmetric to highly asym metric, and most fit well with Bentler-Fano profiles. The observed lin ewidths of near-threshold shape resonances are in strong disagreement with nonadiabatic theoretical calculations. In some instances, broad r esonances coincide almost exactly with the dissociation thresholds, gr eatly affecting the cross sections and dissociation dynamics. An unusu al resonance in HD is observed, in which the H(2s) cross section exhib its a strong interference line shape at the position of the threshold for D(2s) production. [S1050-2947(98)08002-0].