The phenol dimer: Zero-kinetic-energy photoelectron and two-color resonance-enhanced multiphoton ionization spectroscopy

Abstract

The two‐color, two‐photon (1+1’) resonance‐enhanced multiphoton ionization spectrum of the hydrogen‐bonded phenol dimer has been recorded in reasonable agreement with previously reported spectra. However, more features are obtained in this work and this has allowed a more detailed analysis of the spectrum. Five intermolecular vibrations (out of a possible six) are observed for the S₁^donor state, while only two modes are obtained for the S₁^acceptor state. Zero‐kinetic‐energy (ZEKE) photoelectron spectra were recorded via different intermediate vibronic states. The spectrum recorded via the vibrationless level of the S₁^donor state is rich in structure and indicates a large change in the geometry on ionization. Progressions in the intermolecular stretch mode and at least one other mode are obtained. ZEKE spectra were also recorded via a number of S₁^donor vibronic levels, and the S₁^acceptor vibrationless level. The lowest value measured for the ionization energy of the donor is 63 649±4 cm⁻¹ (7.8915±0.0005 eV); this is over 2000 cm⁻¹ lower than the previously reported value. No structure is resolved in the ZEKE spectrum of the acceptor, and it is suggested that this could be due to rapid internal conversion between the S₁^acceptor and S₁^donor states.