New C−H Stretching Vibrational Spectral Features in the Raman Spectra of Gaseous and Liquid Ethanol

Abstract

Traditionally, the Raman spectrum of ethanol in the C-H vibrational stretching region between 2800 cm -1 and 3100 cm -1 had been assigned as three bands of the -CH 2 symmetric stretching, the -CH 3 symmetric stretching, and the -CH 3 antisymmetric stretching. In this report, new Raman spectral features were observed for ethanol and two deuterated ethanols, that is, CD 3 CH 2 OH and CH 3 CD 2 OH, in both gaseous and liquid phases with polarized photoacoustic Raman spectroscopy (PARS) as well as normal Raman spectroscopy. With the aid of depolarization ratio measurements and quantum chemical calculations, different assignments were presented to the complex spectral features in the ethanol Raman spectra. In the gaseous ethanol spectra, the band at ∼2882 cm -1 was assigned to the overlapping symmetric stretching vibrational modes of both -CH 2 and -CH 3 ; the band at ∼2938 cm -1 was assigned to the two symmetric -CH 3 Fermi resonance modes and the weak -CH 2 antisymmetric stretching mode; and the band at ∼2983 cm -1 was assigned to the symmetric -CH 2 Fermi resonance mode and the weak -CH 3 antisymmetric stretching mode. The liquid ethanol spectral features are similar to the gaseous spectra with a much stronger -CH 3 antisymmetric stretching mode and a red shift of about 10 cm -1 , which can be attributed to the effects of solvent interactions. The new assignments of both the gaseous and liquid ethanol spectra not only confirmed the recent results from the sum-frequency generation vibrational spectroscopy studies of the ethanol molecules at the air/liquid interface but the differences in the gaseous and liquid phases, as well as at the interfaces, can also provide detailed experimental evidence in understanding of the molecular interactions and dynamics of the ethanol molecule in different chemical environments.

Polarization effect in tip-enhanced infrared nanospectroscopy studies of the selective Y5 receptor antagonist Lu AA33810

“…In particular, the bands at 2,954 and 2,851 cm −1 in the SEIRA spectrum [45], attributed to the asymmetric CH 3 and symmetric CH 2 stretching modes, are not observed in the p-polarized nanoscale signal. These findings confirm that the intensities of the C-H bands reveal a strong polarization dependence [36,51]. A different spectral pattern is observed for the amino group.…”

Time evolution of the CO2 hydrogenation to fuels over Cu-Zr-SBA-15 catalysts

“…The band of adsorbed methane shows an increasing trend during the reaction. There are also other peaks in these regions which are indexed to other compounds and were detected in very small amounts in GC-MS (as mentioned above): methyl formate (MF) 39,50,51 , ethyl methyl ether (EME) 52 , ethanol [53][54][55] , propane [56][57][58] and butane 59 . This can be the result of random formation in the gas phase rather than the catalyst's activity.…”

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

“…The present work is a continuation of our recent series that aims to give an explicit assignment on vibrational spectrum of alcohol molecules in the C-H stretching region and to provide reliable spectral basis in the other applications. [1][2][3] The C-H functional groups such as -CH, -CH 2 , and -CH 3 exist widely in organic and biological molecules, and the vibration spectroscopy in the C-H stretching region of 2800~3100 cm À1 is one of the extensively employed finger regions for analyzing various dynamical processes or imaging in biology and medicine studies. [4][5][6][7][8][9] This benefits from the two main factors that the C-H stretching vibration is highly localized with no insignificant mixing of other vibrational modes and exhibits the large intensity both in IR and Raman measurements.…”