Picosecond kinetics by exchange broadening in the infrared and Raman. 1. 1,2-Dichloroethane

Spectra of 1,2-dichloroethane, as neat liquid, in solution, and in the solid, were recorded over a wide temperature range. Variation of line shape with temperature was interpreted as due to exchange broadening, caused by interconversion of rotamers, and the Bloch equation could indeed be fitted to the spectra. Spectra of 1,2-dichloroethylene and of 1,1,1-trichloroethane taken as controls showed only slight temperature dependence. Rate constants, in the 10¹²-s^-1 range, and, from them, activation energies and entropies were determined. These were consistent with thermodynamic functions and of reasonable magnitudes.