VIBRATIONAL POPULATION-DYNAMICS OF THE HGI PHOTOFRAGMENT IN ETHANOL SOLUTION

The vibrational population dynamics of HgI fragments in ethanol soluti on, resulting from the 320 nm photolysis of HgI2, are examined both ex perimentally and by a simulation. The experiments reveal an HgI popula tion distribution which rapidly relaxes toward equilibrium. At the ear liest times, the HgI exhibits vibrational coherent wave-packet motion that dephases with a time constant of ca. 1 ps. These data are used to gain insight into the character of the solvated potential energy curv es, The population relaxation was adequately reproduced by master equa tions which were formulated to incorporate the HgI anharmonicity and a solvent frequency dependent friction, This treatment characterizes th e spontaneous vibrational relaxation timescale for the n''=1-->0 trans ition to be ca. 3 ps, and is used to identify the relaxation rate cons tants for all other HgI level pairs. The simulations estimate that the initial excess energy of HgI is centered at n''not similar to 10 whic h corresponds to a total excess energy of ca. 1050 cm(-1). (C) 1995 Am erican Institute of Physics.