Far-wing excitation study of the reactions in the Hg-H₂ collisional quasimolecules. I. Transit-state selectivity in HgH formation and three-body dissociation

Laser-pump/probe and double-beam absorption/dispersion approaches have been applied to the far wings of the Hg ³P₁-¹S₀ resonance line broadened by collisions with H₂. Absolute reduced absorption coefficients of the Hg-H₂ quasimolecules have been determined as a function of the wave-number shift A from the resonance-line center both in the red and blue wings. Decay probabilities of the excited Hg*(³P₁)-H₂ quasimolecule into the reactive channel (HgH formation) or into the elastic channel (Hg*(³P₁) formation) have been determined as a function of A both for the red-wing excited à and blue-wing excited B̃ states. The rest of these decay probabilities have been attributed to three-body dissociation Hg(¹S₀)+H+H. These results indicate that (a) the Ã-state surface serves more effectively in HgH formation than the B̃-state surface by a factor of about 2.3; but (b) three-body dissociation, in turn, proceeds far more efficiently on the B̃-state surface than on the Ã-state surface. Discussions about the. energy barriers and the orbital correlations for HgH formation are presented, based on the Δ dependence of these decaying probabilities.