The Delta v=3, 4, and 5 vibrational overtones and conformations of the hydroxyl group of isobutyl alcohol

The O-H stretching Deltav = 3, 4, and 5 vibrational overtone spectra of iso butyl alcohol (isobutanol, 2-methyl-1-propanol) are measured by using cavit y ring-down spectroscopy (CRDS), where three bonds are observed for each vi brational level. They are assigned to the O-H stretching vibrational absorp tion of the three kinds of conformations of the hydroxyl group and further confirmed by density function theory (DFT) calculations using highly accura te B3LYP/6-31+G(d,p) and 6-311+G(d,p) levels. The experimental mechanical f requencies omega (e), anharmonicities omega (e)chi (e), and dissociation en ergies D are evaluated by the local mode theory. The band intensities of ea ch band are obtained as well. The calculated O-H stretching Deltav = 1, 3, 3, and 5 spectra are simulated by Lorentzian-Gaussian sum function in order to fit the experimental spectra. The molecular vibrational abundance and O -H stretching frequencies of different vibrations of the calculated molecul ar conformations are in agreement with the experimental results.