Pulsed field ionization-ZEKE spectroscopy of cresoles and their aqueous complexes: Internal rotation of methyl group and intermolecular vibrations

Abstract

Pulsed field ionization-ZEKE photoelectron spectroscopy and (1+1) R2PI spectroscopy have been applied to the cis- and trans-m-cresol ·H₂O clusters. The internal rotational structure in the S₁ state has been re-assigned, and the potential curve has been determined for the cluster. The PFI-ZEKE spectra of the cis- and trans-isomers show low-frequency bands up to 1000 cm⁻¹ above the adiabatic ionization potential IP₀. The low-frequency bands are assigned to the internal rotation of the methyl group, the intermolecular stretching and their combination bands in the m-cresol·H₂O cluster cation. Level energies and relative transition intensities are reproduced well by a one-dimensional rotor model with a three-fold axis potential. Potential curves for the internal rotation have been determined for both cis- and trans-isomers of m-cresol ·H₂O cations. The effect of the cluster formation upon the internal methyl rotation, and the interaction between the methyl rotation and the intermolecular vibration are discussed.