Overlapping spectral features and new assignment of 2-propanol in the C-H stretching region

The vibrational spectra of gaseous and liquid 2-propanol in the C-H stretching region of 2800 ~ 3100 cm(-1) were investigated by polarized photoacoustic Raman spectroscopy and conventional Raman spectroscopy, respectively. Using two deuterated samples, that is, CH3CDOHCH3 and CD3CHOHCD3, the overlapping spectral features between the CH and CH3 groups were identified. With the aid of depolarization ratio measurements and density functional theory calculations, a new spectral assignment was presented. In the gas phase, the band at 2884 cm(-1) was assigned to the overlapping of one CH3 Fermi resonance mode and a CH stretching of gauche conformer. The bands at 2917 and 2933 cm(-1) were assigned to another two CH3 Fermi resonance modes, but the latter includes weak contribution from CH stretching of trans conformer. The bands at 2950 and 2983 cm(-1) were assigned to CH3 symmetric and antisymmetric stretching, respectively. The spectral features of liquid 2-propanol are similar to those in the gas phase except for the blue shift of CH and the red shift of CH3 band positions, which can be attributed to the intermolecular interaction in the liquid state. The new assignments not only clarify the confusions in previous studies from different spectral methods but also provide the reliable groundwork on spectral application of 2-propanol in the futures. Copyright (c) 2014 John Wiley & Sons, Ltd.