Ionization-induced pi arrow right H site-switching in phenol-CH sub(4) complexes studied using IR dip spectroscopy

IR spectra of phenol-CH sub(4) complexes generated in a supersonic expansion were measured before and after photoionization. The IR spectrum before ionization shows the free OH stretching vibration ( nu sub(OH)) and the structure of neutral phenol-CH sub(4) in the electronic ground state (S sub(0)) is assigned to a pi -bound geometry, in which the CH sub(4) ligand is located above the phenol ring. The IR spectrum after ionization to the cationic ground state (D sub(0)) exhibits a red shifted nu sub(OH) band assigned to a hydrogen-bonded cationic structure, in which the CH sub(4) ligand binds to the phenolic OH group. In contrast to phenol-Ar/Kr, the observed ionization-induced pi arrow right H migration has unity yield for CH sub(4). This difference is attributed to intracluster vibrational energy redistribution processes.