Size-selected vibrational spectra of phenol-(H2O)n (n=1–4) clusters observed by IR–UV double resonance and stimulated Raman-UV double resonance spectroscopies

Abstract

OH and CH stretching vibrations of bare phenol, phenol-(H2O)n clusters (n=1–4), and partially deuterated clusters in the S0 state were observed by using IR–UV double resonance and stimulated Raman-UV double resonance spectroscopies. Characteristic spectral features of the OH stretching vibrations of the phenol as well as of the H2O sites were observed, which are directly related to their structures. The cluster structures were investigated by comparing the observed spectra with the calculated ones obtained by the ab initio molecular orbital calculation with (self-consistent field) SCF 6-31G and SCF 6-31G* basis sets given by Watanabe and Iwata. It was found that for the clusters with n≥2, the isomer of ring form hydrogen-bonded structure is most stable and the simulated IR spectra based on the calculated structure showed good agreements with the observed ones. For a particular cluster, which was assigned as an isomer of the n=4 cluster, an anomalous IR spectrum was observed. Two forms of the isomer are proposed with respect to the structure of water moiety: (1) an ‘‘ice’’ structure and (2) an ‘‘ion-pair’’ structure. The relative IR absorption cross sections of each bands were also investigated for the clusters with n=1 to 4. It was found that the IR absorption cross section of the phenolic OH stretching vibration of the n=1 cluster increases by a factor of 6 compared to that of bare phenol and it further increases with the cluster size.

Vibrational Spectroscopy of Gas Phase Functional Molecules and Their Complexes Cooled in Supersonic Beams

“…The weak and broad bands at ~3200 cm -1 are due to the overlapped transitions of the aromatic CH stretches. One noticeable point in the IR spectrum of L-Phe-(H 2 O) 2 is that the frequency shift of the carboxyl OH stretch with respect to bare L-Phe is as large as 580 cm -1 , which is more than twice the red-shift of the OH stretch of phenol-(H 2 O) 2 (Watanabe et al, 1996), indicating that the carboxyl OH is considerably weakened under the hydration with two waters. This can be regarded as favorable for the proton transfer to take place in zwitter-ion formation.…”

Hydrogen Bonding in Aromatic Alcohol-Water Clusters: A Brief Review

“…The phenol-(H 2 O) n clusters have been studied most intensively by many investigators [15][16][17][18][19][20][21][22] as the prototypical system for organic alcohol-water cluster. As depicted in Figure 1, the role of the OH group in the phenol-(H 2 O) n cluster can be either proton-donating or -accepting.…”

“…Therefore, systematic study on the hydrogen bond can reveal invaluable information for the structure and biochemical activity of protein. Since there are extremely many solvent molecules in the solution phase, however, it is more useful to study the hydrogen bonding in the clusters [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] consisting of a solute and a few solvent molecules.…”

Computational Study of Catechol-(H?O)?(n=1-3) Clusters

“…Since there are enormous number of solvent molecules in solution phase, they cannot explicitly be treated except by employing the approximations based on polarizable continuum model, 1,2 which is still being developed. Alternatively, the solution phase may be approximated as clusters, [3][4][5][6][7][8][9][10][11][12][13][14][15][16] in which a number of solvent molecules surround the solute to form a certain configuration. The properties of solution depending on the arrangement of solvent molecules around the solute may be efficiently studied by employing this approach.…”