INTERMOLECULAR BONDING AND VIBRATIONS OF 2-NAPHTHOL.H2O (D(2)O)

A combined experimental and theoretical study of the 2-naphthol.H2O/D2 O system was performed. Two different rotamers of 2-naphthol (2-hydrox ynaphthalene, 2HN) exist with the O-H bond in cis- and trans-position relative to the naphthalene frame. Using Hartree-Fock (HF) calculation s with the 6-31G(d,p) basis set, fully energy-minimized geometries wer e computed for both cis- and trans-2HN.H2O of (a) the equilibrium stru ctures with trans-linear H-bond arrangement and C(s) symmetry and (b) the lowest-energy transition states for H atom exchange on the H2O sub unit, which have a nonplanar C1 symmetry. Both equilibrium and transit ion state structures are similar to the corresponding phenol.H2O geome tries. The H-bond stabilization energies with zero point energy correc tions included are almost-equal-to 5.7 kcal/mol for both rotamers, alm ost-equal-to 2.3 kcal/mol stronger than for the water dimer, and corre spond closely to the binding energy calculated for phenol.H2O at the s ame level of theory. Extension of the aromatic pi-system therefore har dly affects the H-bonding conditions. The barrier height to internal r otation around the H-bond only amounts to 0.5 kcal/mol. Harmonic vibra tional analysis was carried out at these stationary points on the HF/6 -31G(d,p) potential energy surface with focus on the six intermolecula r modes. The potential energy distributions and M-matrices reflect con siderable mode scrambling for the deuterated isotopomers. For the a' i ntermolecular modes anharmonic corrections to the harmonic frequencies were evaluated. The beta2 wag mode shows the largest anharmonic contr ibutions. For the torsional mode tau (H2O H-atom exchange coordinate) the vibrational level structure in an appropriate periodic potential w as 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 intermolecula r frequency range is given, based on the calculations. The predicted a nd measured vibrational frequencies are compared and differences discu ssed.