ZERO KINETIC ENERGY PHOTOELECTRON (ZEKE) SPECTROSCOPY OF THE HETERO TRIMER PHENOL-WATER-ARGON: INTERACTION BETWEEN A HYDROGEN BOND AND A VAN DER WALLS BOND

Abstract

The hetero trimer 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 $(1 + 1^{\prime})$ resonance-enhanced multiphoton ionization (REMPI) spectrum of the $S_{1}$ state shows striking differences compared to the spectrum of the corresponding complex without water. The zero kinetic energy photoelectron (ZEKE) spectrum of phenol-water-Ar represents the first ZEKE spectrum of a complex containing three different species as well as two different intermolecular bonds. From that spectrum, an accurate ionization energy and the frequencies of three van der Waals vibrations of the ionic ground state have been obtained. The 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. From sharp steps in the photoionization efficiency (PIE) spectra of phenol-water-Ar and the fragment complex phenol-water an upper limit for the dissociation energy of the van der Waals bond in the ionic state has been obtained, and from that value upper limits for the binding energies in the both neutral states $(S_{0} S_{1})$ could be derived. For comparison, REMPI and PIE spectra have also been recorded for phenol-water-Ne. Finally, a mass-analyzed threshold ionization (MATI) 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.