VIBRATIONAL-RELAXATION OF THE NU(C=O) MODE OF ETHYL TRICHLOROACETATE IN SOLUTION

An analysis of the IR and Raman band shapes corresponding to the carbo nyl stretching mode, nu(C-0), of ethyl trichloroacetate in hexane, car bon tetrachloride, carbon disulfide and chloroform solutions provides the vibrational and reorientational correlation functions. The vibrati onal processes in the relaxation of this mode seem to be dominant on l ong timescales (from ca. 0.4 ps), the vibrational width increases when the solvent changes in the order C6H14 < CS2 < CCl4 < CHCl3. An inter mediate modulation regime is observed. The isolated binary collision ( IBC) model does not account for the values of the vibrational width, b ut it predicts the observed trend in non-polar solvents. The reorienta tional motion is less hindered in CS2 and C6H14, but its contribution to the relaxation in CHCl3 solution is negligible at long times. A com parative study on the esters CX3CO2Et (X = H, F and Cl) reveals that t he relaxation is increasingly efficient when the CX3 group varies in t he order CCl3 < CF3 < CH3.