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Intermolecular bonding and vibrations of 2-naphthol·H2O (D2O)

Schütz, Martin
Leutwyler, Samuel
Fischer, Thomas
Published in Journal of Chemical Physics. 1993, vol. 99, no. 3, p. 1469-13
Abstract A combined experimental and theoretical study of the 2‐naphthol⋅H2O/D2O system was performed. Two different rotamers of 2‐naphthol (2‐hydroxynaphthalene, 2HN) exist with the O–H bond in cis‐ and trans‐position relative to the naphthalene frame. Using Hartree–Fock (HF) calculations with the 6‐31G(d,p) basis set, fully energy‐minimized geometries were computed for both cis‐ and trans‐2HN⋅H2O of (a) the equilibrium structures with trans‐linear H‐bond arrangement and Cs symmetry and (b) the lowest‐energy transition states for H atom exchange on the H2O subunit, which have a nonplanar C1 symmetry. Both equilibrium and transition state structures are similar to the corresponding phenol⋅H2O geometries. The H‐bond stabilization energies with zero point energy corrections included are ≊5.7 kcal/mol for both rotamers, ≊2.3 kcal/mol stronger than for the water dimer, and correspond closely to the binding energy calculated for phenol⋅H2O at the same level of theory. Extension of the aromatic Π‐system therefore hardly affects the H‐bonding conditions. The barrier height to internal rotation around the H‐bond only amounts to 0.5 kcal/mol. Harmonic vibrational analysis was carried out at these stationary points on the HF/6‐31G(d,p) potential energy surface with focus on the six intermolecular modes. The potential energy distributions and M‐matrices reflect considerable mode scrambling for the deuterated isotopomers. For the a' intermolecular modes anharmonic corrections to the harmonic frequencies were evaluated. The β2 wag mode shows the largest anharmonic contributions. For the torsional mode τ (H2O H‐atom exchange coordinate) the vibrational level structure in an appropriate periodic potential was calculated. On the experimental side resonant‐two‐photon ionization and dispersed fluorescence emission spectra of 2HN⋅H2O and d‐2HN⋅D2O were measured. A detailed assignment of the bands in the intermolecular frequency range is given, based on the calculations. The predicted and measured vibrational frequencies are compared and differences discussed.
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Deposited on : 2011-03-18

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