Infrared spectroscopic structure investigations of 1-hexanol: dependence on high pressure

Abstract

Infrared spectra of 1-hexanol in PCFE (=poly-(chlor-trifluorethylene)-oil) at high pressures are discussed. The absorption band assigned to the OH stretching vibration of the H-bonded OH group is split into two bands at high pressures. The splitting indicates an OH⋯OH⋯ chain structure. The correlation of the in-phase and out-of-phase OH stretching vibrations ( v 1, v 2) with the different force constants results from the normal coordinate analysis of a linear chain. The higher frequency band must be assigned to the in-phase vibration v 1. The decoupled OH vibration ( v OH), the coupled and decoupled H-bond vibration ( v 5, v 00) and all force constants are calculated from the observed frequencies v 1 and v 2. The force constants k 1 and k 2 relate to the OH and H⋯O bonds. respectively, and the interaction force constants k 12 and k 21 change characteristically with the pressure. The comparison of the fundamental with the overtone spectra allows calculation of the combination anharmonicity constant x 12 which corresponds to the anharmonicity constant of the decoupled OH vibration x OH.