VIBRATIONAL SPECTROSCOPY OF THE PHENOL-ETHANOL CATION

The hydrogen-bonded phenol-ethanol complex has been studied using both two-color resonant-enhanced multiphoton ionization (REMPI) and zero-kinetic-energy (ZEKE) photoelectron spectroscopy. The REMPI spectrum shows vibrational structure which can be assigned to low-frequency intermolecular modes on the S1 origin and in combination with intramolecular (phenol-localized) vibrations of the S1 electronic state: a reinterpretation of the low-energy region of the REMPI spectrum gives the frequency of the intermolecular stretch in the S1 state as 162 cm-1. ZEKE spectra were recorded using different vibrational excitations of the S1 state as the intermediate level. These spectra show different vibrational excitation of the ion due to modified Franck-Condon factors for the ionization step. The ZEKE spectra allow all six intermolecular modes of the phenol-ethanol cation to be determined. The ionization energy is determined accurately as 62 901 +/- 5 cm-1 [7.7988 +/- 0.0006 eV] and the increase in binding energy between the S0 and the ionic ground state is derived as 5727 +/- 10 cm-1, giving an approximate value for the ionic complex bond energy of 8000 cm-1 [ca. 1 eV].