Internal Rotation and Intermolecular Vibrations of the Phenol−Methanol Cluster:  A Comparison of Spectroscopic Results and Ab Initio Theory

Abstract

The vibronic spectra of five deuterated species of the binary phenol−methanol cluster are compared to the intermolecular vibrational frequencies of an ab initio-based normal-mode analysis. Isotopomers with equal mass could be distinguished experimentally using spectral hole-burning spectroscopy. The vibronic bands of phenol−methanol are split into A and E components because of the internal rotation of the methyl group. This torsional splitting is increased for three of the intermolecular vibrations because of coupling to the large-amplitude motion. Guided by comparison to an ab initio normal-mode analysis and by the torsional splitting of some of the vibronic bands, a complete intermolecular vibrational assignment for the phenol−methanol cluster is presented.

Determination of the intermolecular geometry of the phenol–methanol cluster

“…This splitting was observed in the high resolution spectrum of the electronic origin of phenol (CH 3 OH) 1 , as well as in the hole burning spectra, which were obtained via excitation of a single torsional component in the vibronic spectrum. 7 All isotopomers of phenol-methanol dealt with in this publication, belong to the molecular symmetry group G 3 . The lowest torsional wave function of a threefold internal rotor in the MS group G 3 transforms as A, the next transforms as E. The torsional wave functions can be expanded in the basis of free rotor functions:…”

“…The vibrational frequencies of the phenol-methanol cluster in the electronic ground state were determined by dispersed fluorescence spectroscopy by Abe et al 2 The fluorescence excitation spectrum was measured and the vibronic bands assigned by Abe et al 1 Recently, a joint spectroscopic and ab initio study on the intermolecular vibrations of several isotopomers of phenol-methanol was published by our group. 7 A theoretical analysis of the intermolecular vibrations in the electronic ground state was given by Gerhards et al 4 They predicted a translinear geometry, as in the case of the phenol-water cluster. Courty et al presented a structure of the cluster in which the methanolic methyl group is bent towards the aromatic ring resulting in a nonlinear hydrogen bond.…”

Torsional Barriers in Aromatic Molecular Clusters as Probe of the Electronic Properties of the Chromophore

“…[31] Axes and displacement vectors for both motions nearly coincide as has been shown for the phenol-methanol cluster as well. [25] Thus, a strong coupling of both motions is plausible. The barrier to methyl torsion in free methanol from microwave spectroscopy is 376.8 cm…”

“…Symmetry-labeled hole-burning spectroscopy has been performed, but no bands were found because of pure excitation of the torsional motion. [25] The perturbation terms and AE splitting for phenol-(CH 3 OH) are taken from ref. [26], those for phenol(CD 3 OH) from Westphal et al [27] The perturbation terms for phenol(CD 3 OH) from ref.…”

A Theoretical Study of 1‐D and 2‐D Helium Lattices

“…[1][2][3][4][5][6] Only recently in the past decade, computational study of assembly of atoms and molecules have received growing attention of chemists and physicists. [7][8][9][10][11][12][13][14][15][16][17] In this line, ab initio study of helium dimers and clusters both as interesting chemical species and as prototype systems for the evaluation of the newly developed computational methods have also been studied extensively. [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32] However, none of these computational studies has so far aimed at the ab initio calculation of the bulk properties of liquids and solids.…”