RELAXATION OF THE PRODUCT STATE COHERENCE GENERATED THROUGH THE PHOTOLYSIS OF HGI2 IN SOLUTION

Experimental results are presented for wave packet dynamics of the HEI molecules produced through the impulsive photolysis of HgI2 in ethano l solution. The results demonstrate that the HgI is formed in a vibrat ional superposition state. The phase of the beats fit to a value of 0. 9 pi. This information is used to estimate the frequency of a transiti on state vibration of the HgI2 reactive state in solution. Both the os cillation frequency and decay rate exhibit a probe wavelength dependen ce. This is described as a result of each of the finite probe spectral bandwidths interrogating a specific set of vibrational eigenstates. T he anharmonicity of HgI leads to a distinct oscillatory signal for eac h of the probes used. From this an approximate assignment of the level pairs being sampled by each probe is obtained. This information is us ed to construct solvated potential energy surfaces consistent with the data. The level dependent relaxation was not interpretable by a simpl e Bloch-type picture, in which each coherence is characterized by a co mplex frequency. A quantum mechanical relaxation matrix including cohe rence transfer terms adequately modeled the observed coherence retenti on. The data also show that an energy dependent pure dephasing rate is required for the anharmonic HgI level pairs. Other aspects of solvate d wave packet dynamics are discussed. (C) 1996 American Institute of P hysics.