The structure of phenol-Ar(n) (n=1,2) clusters in their S(0) and S(1) states.

The structures of the van der Waals bonded complexes of phenol with one and two argon atoms have been determined using rotationally resolved electronic spectroscopy of the S(1)<--S(0) transition. The experimentally determined structural parameters were compared to the results of quantum chemical calculations that are capable of properly describing dispersive interactions in the clusters. It was found that both complexes have pi-bound configurations, with the phenol-Ar(2) complex adopting a symmetric (1mid R:1) structure. The distances of the argon atoms to the aromatic plane in the electronic ground state of the n=1 and n=2 clusters are 353 and 355 pm, respectively. Resonance-enhanced multiphoton ionization spectroscopy was used to measure intermolecular vibrational frequencies in the S(1) state and Franck-Condon simulations were performed to confirm the structure of the phenol-Ar(2) cluster. These were found to be in excellent agreement with the (1mid R:1) configuration.