An experimental and computational study of the effect of aqueous solution on the multiphoton ionisation photoelectron spectrum of phenol

Faraday Discuss. 2019 Dec 16;221(0):202-218. doi: 10.1039/c9fd00079h.

Abstract

We revisit the photoelectron spectroscopy of aqueous phenol in an effort to improve our understanding of the impact of inhomogeneous broadening and inelastic scattering on solution-phase photoelectron spectra. Following resonance-enhanced multiphoton ionisation via the 11ππ* and 11πσ* states of phenol, we observe 11ππ*-D0/D1 ionisation and competing direct S0-D0/D1 ionisation. Following resonance-enhanced multiphoton ionisation via the 21ππ* state, we observe the signature of solvated electrons. By comparing the photoelectron spectra of aqueous phenol with those of gas-phase phenol, we find that inelastic scattering results in peak shifts with similar values to those that have been observed in photoelectron spectra of solvated electrons, highlighting the need for a robust way of deconvoluting the effect of inelastic scattering from liquid-phase photoelectron spectra. We also present a computational strategy for calculating vertical ionisation energies using a quantum-mechanics/effective fragmentation potential (QM/EFP) approach, in which we find that optimising the configurations obtained from molecular dynamics simulations and using the [phenol·(H2O)5]QM[(H2O)n≥250]EFP (B3LYP/aug-cc-pvdz) method gives good agreement with experiment.