ANISOTROPY MEASUREMENTS OF SOLVATED HGI2 DISSOCIATION - TRANSITION-STATE AND FRAGMENT ROTATIONAL-DYNAMICS

Pump-probe anisotropy measurements of HgI2 photodissociation in ethano l were carried out. The reactive motion from electronically excited Hg I2 toward HEI and I is clearly evident in the signal. The subsequent r andomization of the HgI orientational distribution occurs in the bipha sic manner typical for some other diatomic molecules, with a 500-fs co mponent that has an inertial motion contribution and a slow (8-10-ps) diffusive component. Interpretations of these regions were assisted by molecular dynamics simulations, which also were used to show that the rotational energy relaxation would be very fast in this system. The m agnitudes of the anisotropies at different pump wavelengths show that the near-UV absorption of HgI2 involves overlapping (1) Sigma(+) --> ( 1) Sigma(-) and (1) Sigma(+) --> (1) Pi transitions, consistent with m agnetic circular dichroism (MCD) measurements. The anisotropy decay sh ows oscillations which an proposed to arise from oscillations in the v olume and moment of inertia as the vibrational wavepacket moves in the anharmonic HEI potential.