Experimental and theoretical study of the vibrational spectra of halothane

MP2 and B3LYP calculations carried out with the 6-311++G(df,pd) basis set show that the staggered structure of halothane (2-bromo-2-chloro-1,1,1-trifluoroethane) is more stable than the eclipsed one. Results of natural bond orbital calculations for both structures are discussed. The experimental IR and Raman spectra of halothane pure and dissolved in carbon tetrachloride are investigated. The harmonic vibrational frequencies, and IR and Raman intensities are calculated with the B3LYP method using the same basis set. The detailed assignment of the fundamental vibrations of halothane is made on the basis of the calculated potential energy distribution, PED. The near-IR spectra are investigated between 4000 and 9000 cm−1. The frequencies of the fundamental, first and second overtone have allowed us to estimate the anharmonicity constants of the ν(CH) stretching vibration. The frequency of this vibration corrected for anharmonicity is in good agreement with the B3LYP one. The experimental spectra show that the ν(CH) vibration of halothane, in complexes with acetone or dioxane, is red-shifted by a few wavenumbers. Complex formation increases the anharmonicity of the ν(CH) vibration.