Intermolecular vibration and internal rotation of a methyl group in acetanilide·Ar: a ZEKE photoelectron spectroscopy study

Two-color REMPI and ZEKE photoelectron spectra are presented for the trans-acetanilide·Ar complex. Methyl rotor features are prominent in the cluster spectra and appear with unperturbed frequencies and intensities compared to acetanilide, indicating that the argon atom exerts little influence on the methyl rotor from its van der Waals binding position above the aromatic ring. Analysis of the spectra allowed the determination of the S1 and D0 barrier heights (50 and 320 cm−1), and the S0 and S1 0a–1e splitting (3.9 and 2.0 cm−1).