Vibrational anharmonicity of acetic acid studied by matrix-isolation near-infrared spectroscopy and DFT calculation

Near-infrared (NIR) spectra of acetic acid in a low-temperature argon matrix were measured in the range of 3950-12 000 cm−1, where ≈40 sharp combination and overtone bands were observed and assigned. The first and second overtone bands for the OH stretching mode, assigned by use of the observed H-D isotope shifts and density functional theory calculations at the B3LYP/6-31++G** level. The observed wavenumbers were essentially reproduced by the anharmonic wavenumbers estimated by the Gaussian 03 program extended to the NIR region.