VIBRATIONAL-RELAXATION OF I-2 IN COMPLEXING SOLVENTS - THE ROLE OF SOLVENT-SOLUTE ATTRACTIVE FORCES

Femtosecond transient absorption studies of I-2-arene complexes, with arene=hexamethylbenzene (HMB), mesitylene (MST), or m-xylene (mX), are used to investigate the effect of solvent-solute attractive forces up on the rate of vibrational relaxation in solution. Comparison of measu rements on I-2-MST complexes in neat mesitylene and I2-MST complexes d iluted in carbontetrachloride demonstrate that binary solvent-solute a ttractive forces control the rate of vibrational relaxation in this pr ototypical model of diatomic vibrational relaxation. The data obtained for different arenes demonstrate that the rate of I? relaxation incre ases with the magnitude of the h-arene attractive interaction. I-2-HMB relaxes much faster than I-2 in MST or mX. The results of these exper iments are discussed in terms of both isolated binary collision and in stantaneous normal mode models for vibrational relaxation. (C) 1998 Am erican Institute of Physics. [S0021-9606(98)01245-8].