Association and the assignment of the OH overtones in hydrogen bonded alcohols

Abstract

The long-standing problem of the assignment of the first overtone of the OH stretching vibration of hydrogen bonded alcohols is examined for the cases of methanol, ethanol, and tertiary butanol. The spectra of the related deuterated alcohols were measured and isotopic isolation experiments were carried out at temperatures ranging from 25° to − 190°C. Dilute solutions were studied as well as the pure liquids. For the latter the second overtones were also measured. The first OH overtones, although overlapped by CH + OH combination bands were definitely identified and the anharmonicity constants were determined. They show a moderate but appreciable increase with respect to free OH stretching vibrations. Bands due to simultaneous excitation or coupling of two contiguous OH groups bound together by hydrogen bonds are also present.