Raman spectra of gases. XIII. Two-quantum torsional transitions in some dihalo- and trihaloethanes

Methyl torsional overtones (Δν=2) have been observed for CH3CHCl2, CD3CDCl2, CH3CHBr2, CH3CCl3, CD3CCl3, CH3CBr3, CH3CCl2F, CH3CF2Br, and CH3CBr2Cl in the Raman effect. From the observed frequency shifts, barriers to internal rotation have been calculated to be 4.13, 4.13, 4.33, 5.43, 5.40, 5.78, 4.42, 5.06, and 5.70 kcal/mole, respectively. Some of these barriers have never been determined for the gas phase. Trends of barrier height as a function of halogen substitution are discussed for chlorine and bromine substitution.