The hydrogen-bonded 1:1 phenol-dimethyl ether complex is studied in a skimmed supersonic jet. Two-photon, two-color resonance-enhanced multiphoton ionization (1 + 1' REMPI) spectroscopy is used to probe the first excited singlet (S-1) state, and the spectra obtained here show that the analysis of a previously recorded laser-induced fluorescence excitation spectrum was partially erroneous. The origin of the S-1 <-- S-0 transition is now identified at 35 843.6 cm(-1); the intermolecular stretch of the S-1 state is determined (for the first time) as 141 cm(-1); other inter- and intramolecular vibrational structures are also observed and analyzed. Particular S-1 state vibrational levels are selected and then used as intermediate resonances for the zero-kinetic-energy photoelectron (ZEKE) spectroscopic studies. This technique allows the measurement of the intermolecular modes of the cationic complex. These measurements also allow the first determination of the ionization energy as 62 604 +/- 5 cm(-1) (7.7620 +/- 0.0006 eV). The intermolecular bond in the cation is over 6000 cm(-1) more stable than that in the neutral complex. A qualitative interpretation of the chemical bonding changes between this complex and other phenol-containing hydrogen-bonded complexes is presented.

1.T.G.Wright, E. Cordes, O. Dopfer and K. $MuUller-Dethlefs, J. Chem. Soc. Faraday Trans., 89, 1609 (1993); K. $MuUller-Dethlefs, O. Dopfer and T.G. Wright, Chem, Rev. in press (1994).

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].

The two-colour, two-photon (1 + 1') resonance-enhanced multiphoton ionisation (REMPI) spectrum of the S1 state of the hydrogen-bonded phenol-methanol complex has been recorded. The region around the S1 origin is in good agreement with previously reported spectra. In this work, further discussion of this region is presented and all the observed spectral features are attributed to intermolecular vibrations (and combinations) of a single conformal isomer. Additionally, further bands have been observed in the higher energy region and are assigned to intramolecular (phenol-localised) modes in combination with intermolecular vibrations.Zero-kinetic-energy (ZEKE) photoelectron spectra have been recorded using different intermediate vibrational levels in the S1 state. The spectrum recorded via the vibrationless level of the S1 state shows beautiful structure and indicates a substantial change in complex geometry on ionisation. The observed structure is dominated by progressions of a low-frequency intermolecular bending vibration (34 cm-1) in combination with other intermolecular vibrations. In particular, the intermolecular stretch (278 cm-1) demonstrates a progression, each component of which is in combination with progressions of the low-frequency bending mode. Excitation via other intermediate, intermolecular vibronic states also gives rise to structured spectra and these lead to the assignment of the six intermolecular vibrational frequencies of the phenol-methanol cation. In contrast, excitation via the intramolecular phenol nu6a level gives rise to a featureless spectrum. It is proposed that the latter observation is due to rapid intramolecular vibrational relaxation (IVR) in the S1 state. The energy of the lowest band observed in the ZEKE spectra exciting via the S1 vibrationless level, the intermolecular stretch and also two other intermolecular vibrations, in all cases allowed a (field-corrected) adiabatic ionisation energy of 63207 +/- 4 cm-1 (7.8367 +/- 0.0005 eV) to be derived.