Raman and far infrared spectra, structural parameters, and ab initio calculations on acetyl chloride

The Raman spectra (3100–10 cm−1) of gaseous, liquid and solid acetyl chloride (CH3CClO) and acetyl‐d3 chloride (CD3CClO) were recorded and qualitative depolarization values were obtained for the liquid. Additionally, the infrared spectra (3100–50 cm−1) of the gas and solid were recorded. A complete vibrational assignment is proposed for both isotopomers. The assignments are supported by normal coordinate calculations utilizing force constants from the ab initio calculations. The methyl torsion is observed at 162.8 cm−1 from which a threefold barrier of internal rotation of 622 cm−1 (1779 cal mol−1) is calculated. Utilizing the frequencies for the isolated CH stretching frequencies from the CHD2CClO molecule, r0 parameters of 1.093 and 1.096 Å were obtained for the CHs and CHa bond distances. The heavy atom r0 structural parameters were obtained from previously reported rotational constants from ten isotopomers. Ab initio calculations were carried out employing the RHF/3–21G*, RHF/6–31G* and MP2/6–31G* basis sets to obtain the vibrational frequencies, force constants, infrared and Raman intensities, structural parameters and barriers to internal rotation. The theoretical results were compared with the experimental quantities when appropriate.