Zero kinetic energy photoelectron (ZEKE) spectroscopy of the heterotrimer phenol-water-argon: Interaction between a hydrogen bond and a van der Waals bond Original Research Article

The heterotrimer phenol -water- Ar, a complex containing two different types of intermolecular bonds — a van der Waals bond and a hydrogen bond — has been studied in a supersonic jet with various spectroscopic techniques. The two-photon, two-color (1 + 1′) resonance-enhanced multiphoton ionization (REMPI) spectrum of the S1 state shows striking differences compared to the spectrum of the corresponding complex without water. From the zero kinetic energy photoelectron (ZEKE) spectrum an accurate ionization energy and the frequencies of all three van der Waals vibrations of the ionic ground state have been obtained. Comparison of the ZEKE and REMPI spectra of phenol-water-Ar with the corresponding spectra of phenol-Ar and phenol-water indicates that the stronger hydrogen bond noticeably influences the weaker van der Waals bond, while vice versa the hydrogen bond is nearly not affected by the additional van der Waals bond. Sharp steps in the photoionization efficiency (PIE) spectra of phenol-water-Ar and the fragment complex phenol-water provide an upper limit for the dissociation energy of the van der Waals bond in the ionic state, and from this value upper limits for the binding energies in both neutral states (S0, S1) have been derived. For comparison, REMPI and PIE spectra have also been recorded for phenol -water-Ne. Finally, the first mass-analyzed threshold ionization spectrum of a hydrogen-bonded complex, namely phenol-water, has been recorded in order to demonstrate that this technique can also be utilized for such type of complexes.