Photoelectron spectroscopy of liquids up to 21.2 eV

Abstract

Photoelectron spectroscopy of liquids is investigated at variable photon energies up to 10 eV and with rare-gas resonance lines at 11.7 (ArI), 16.8 (NeI), and 21.2 (HeI) eV. Seven liquids are studied: N-methylaniline, N,N′-dimethyl-p-toluidine, formamide, hexamethyl phosphoric triamide, tetraglyme, ethylene glycol, and n-decanol. Energy distribution curves display at the higher photon energies a band structure matching the sequence of bands in the corresponding gas-phase photoelectron spectra. The bands are attributed to emission of unscattered electrons (no loss of kinetic energy to the liquid) whereas the underlying background is ascribed to scattered (in the liquid) electrons. Quantitative treatment based on this interpretation agrees with experiment. Energies characterizing either bulk or surface photoionization are determined within ±0.1 eV. The gas–liquid red shift (0.9 to 1.4 eV) and bulk–surface blue shift (0.5 to 1.3 eV) in photoionization energies are interpreted in terms of electronic polarization of the liquid medium. This is, to our knowledge, the first investigation of liquids by ultraviolet photoelectron spectroscopy above 10 eV.