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

Abstract

The phenol⋅N2 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 where the N2 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±20 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⋅N2 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 π-system of the benzene ring.