Vibrational relaxation of the ν(CO) mode of ethyl trichloroacetate in solution

Abstract

An analysis of the IR and Raman band shapes corresponding to the carbonyl stretching mode, ν(CO), of ethyl trichloroacetate in hexane, carbon tetrachloride, carbon disulfide and chloroform solutions provides the vibrational and reorientational correlation functions. The vibrational processes in the relaxation of this mode seem to be dominant on long timescales (from ca. 0.4 ps), the vibrational width increases when the solvent changes in the order C6H14 < CS2 < CCI4 < CHCI3. An intermediate modulation regime is observed. The isolated binary collision (IBC) model does not account for the values of the vibrational width, but it predicts the observed trend in non-polar solvents. The reorientational motion is less hindered in CS2 and C6H14, but its contribution to the relaxation in CHCI3 solution is negligible at long times. A comparative study on the esters CX3CO2Et (X = H, F and Cl) reveals that the relaxation is increasingly efficient when the CX3 group varies in the order CCl3 < CF3 < CH3.