Anharmonic coupling revealed by the vibrational spectra of solvated protonated methanol: Fermi resonance, combination bands, and isotope effect
Journal
Journal of Physical Chemistry A
Journal Volume
125
Journal Issue
9
Pages
1910-1918
Date Issued
2021
Author(s)
Abstract
Intriguing vibrational features of solvated protonated methanol between 2400-3800 cm-1 are recorded by infrared predissociation spectroscopy. Positions of absorption bands corresponding to OH stretching modes are sensitive to changes in solvation environments, thus leading to changes in these vibrational features. Two anharmonic coupling mechanisms, Fermi resonance (FR) contributed by bending overtones and combination band (CB) associated with intermolecular stretching modes, are known to lead to band splitting of OH stretching fundamentals in solvated hydronium and ammonium. Theoretical analyses based on the ab initio anharmonic algorithm not only well reproduce the experimentally observed features but also elucidate the magnitudes of such couplings and the resulting interplay between these two mechanisms, which provide convincing assignments of the spectral patterns. Moreover, while the hydroxyl group plays the leading role in all the above-mentioned features, the role of the methyl group is also analyzed. Through the H/D isotope substitution, we identify overtones of the methyl-hydroxyl rocking modes and their participation in FR. ? 2021 American Chemical Society. All rights reserved.
Other Subjects
Methanol; Protonation; Resonance; Anharmonic couplings; Combination bands; Fermi resonances; Intermolecular stretching; Isotope substitution; Predissociation spectroscopy; Spectral patterns; Vibrational features; Isotopes
Type
journal article