Evidence for a strong intermolecular bond in the phenol•N2 cation

The phenol.N-2 complex cation has been studied with a combination of two-color resonant zero kinetic energy (ZEKE) and mass analyzed threshold ionization (MATI) spectroscopies to probe the interaction of a polar cation with a quadrupolar solvent molecule. Extended vibrational progressions are observed in three modes which are assigned as the in-plane bend (35 cm(-1)), the stretch (117 cm(-1)). and in-plane wag (130 cm(-1)) intermolecular vibrations, and are consistent with a structure when the NZ forms a directional bond to the phenol OH group in the plane of the aromatic ring. Ab initio calculations at the UMP2/6-31G*, UHF/cc-pVDZ, and UMP2/cc-pVDZ levels of theory support this assignment. The spectra also provide a value for the adiabatic ionization energy (67 423 cm(-1) +/- 4.5 cm(-1)) and an estimate of the dissociation energy of the cluster (1650 +/- cm(-1)) which illustrate that the quadrupolar nitrogen molecule binds considerably more strongly to the phenol cation than a rare gas atom. These results constitute the first report of an aromatic N-2 complex where the interaction can be described in terms of weak hydrogen bonding, rather than in terms of a van der Waals bond to the pi-system of the benzene ring. (C) 1998 American Institute of Physics. [S0021-9606(98)02245-4].