Fourier transform Raman spectrum, vibrational assignment andab initio calculation of methanesulfonic acid in the gas and liquid phases

The Fourier transform Raman spectrum of liquid methanesulfonic acid, CH3SO2OH, was recorded and the spectral data were interpreted in detail. Ab initio calculations were carried out with different basis sets up to MP2/6–311+G(2d,2p), from which structural parameters and conformational stabilities were determined. The spectrum of the liquid is interpreted on the basis of a dimer structure with Ci symmetry. Normal coordinate calculations were carried out for both the monomer and dimer and the results indicate that the differences in wavenumbers for the normal vibrations for the monomer and dimer are relatively small. These calculations also indicate that the dimer structure is a reasonable model for the associated molecules of methanesulfonic acid in the liquid phase. The spectroscopic and theoretical results are compared with the corresponding quantities for some similar molecules.