New spectral assignment of n‐propanol in the C―H stretching region

Abstract

The C―H stretching vibration serves as an important probe for characterizing molecular structures and properties of hydrocarbons. In this work, we present a detailed study on gas‐phase Raman spectrum of n‐propanol in the C―H stretching region using stimulated photoacoustic Raman spectroscopy. A complete assignment was carried out with the aid of quantum chemistry calculations and depolarization ratio measurement as well as isotope substitutions, i.e. CH3CD2CD2OH, CD3CH2CD2OH and CD3CD2CH2OH. It is shown that the spectra of three C―H groups of n‐propanol overlap each other because of Fermi resonance coupling and different molecular conformations, leading to complex features that were not determined previously. In addition, the comparisons between the spectra of three isotopologues reveal that the C―H vibrations at different sites of carbon chain exhibit different sensitivity to conformational change of n‐propanol. The CH3 stretching vibration at terminated γ‐carbon is not sensitive whereas the CH2 stretching vibrations at both α‐carbon and β‐carbon atoms are sensitive. Furthermore, Raman spectra of liquid propanol recorded by conventional spontaneous Raman technique are reassigned on the basis of gas‐phase analysis. Copyright © 2016 John Wiley & Sons, Ltd.

Characterizing chemical composition of polyolefin‐based copolymers from spectral features in the C―H stretching region

“…Overall, Snyder assignments need to be revised in view of the more recent studies of vibrational modes of the C―H stretching region. For instance, Liu et al used deuteration to isolate specific Raman signatures of the CH 2 group of the n‐propanol molecule founding that it gives rise to two peaks at 2,854 and 2,873 cm −1 , assigned to Fermi resonance components, along with other two at 2,917 and 2,941 cm −1 , assigned to symmetric stretching, ν S (CH 2 ), see Table . The coupling with other CH 2 groups or the lack of strong intermolecular interactions as occur in polymethylene chains may explain the differences with our work.…”

“…The coupling with other CH 2 groups or the lack of strong intermolecular interactions as occur in polymethylene chains may explain the differences with our work. Antisymmetric stretching modes are observed as weak and broad bands, most likely overlapped by the stronger ν A (CH 2 ) peaks . Therefore, one of the most important differences with Snyder is the assignation of 2,888 cm −1 as ν A (CH 2 ), which, in the framework of Liu, should be most likely assigned as a Fermi resonant component.…”

“…For instance, Wang et al examined several short‐chain alcohols at the liquid/air interface using the sum‐frequency generation (SFG) vibrational spectroscopy, and they found new spectral features of CH 2 and CH 3 groups, which were assigned to Fermi interaction . Very recently, Liu et al published a series of studies using deuteration to isolate specific Raman signatures of the CH, CH 2 , and CH 3 groups in 1‐ and 2‐propanol molecules . Supported by quantum chemistry calculations, the authors discerned overlapping spectral features arising from each of these groups and provided a well‐founded peak assignment.…”

Recent advances in linear and non‐linear Raman spectroscopy. Part XI

“…They present a detailed study on gas‐phase Raman spectrum of n ‐propanol in the C‐H stretching region using stimulated photoacoustic Raman spectroscopy. A complete assignment was carried out with the aid of quantum chemistry calculations and depolarization ratio measurements, as well as isotope substitutions …”

Dielectrophoretic positioning of single nanoparticles on atomic force microscope tips for tip‐enhanced Raman spectroscopy

“…Recently, the applicability of DEP for the attachment of single micrometer sized Polystyrene beads and Ag wires to AFM tips has been reported [29,30], with resulting tip diameters of ß100-200 nm. In order to investigate DNA or protein strand-like samples, nanoparticles with a significantly smaller radius are required as signal enhancers to reduce the probed sample volume to as few molecules as possible.…”