The hydrogen-bonded phenol-ethanol complex has been studied using both
two-color resonant-enhanced multiphoton ionization (REMPI) and zero-k
inetic-energy (ZEKE) photoelectron spectroscopy. The REMPI spectrum sh
ows vibrational structure which can be assigned to low-frequency inter
molecular modes on the S1 origin and in combination with intramolecula
r (phenol-localized) vibrations of the S1 electronic state: a reinterp
retation of the low-energy region of the REMPI spectrum gives the freq
uency of the intermolecular stretch in the S1 state as 162 cm-1. ZEKE
spectra were recorded using different vibrational excitations of the S
1 state as the intermediate level. These spectra show different vibrat
ional excitation of the ion due to modified Franck-Condon factors for
the ionization step. The ZEKE spectra allow all six intermolecular mod
es of the phenol-ethanol cation to be determined. The ionization energ
y 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 groun
d state is derived as 5727 +/- 10 cm-1, giving an approximate value fo
r the ionic complex bond energy of 8000 cm-1 [ca. 1 eV].