Measurement of He I photoelectron spectra of liquid water, formamide and ethylene glycol in fast-flowing microjets

The free surfaces of liquid water, formamide and ethylene glycol are prepared as a microjet in a high vacuum where they are studied by UV photoelectron spectroscopy with He I (hv = 21.22 eV) photons. The low vapour pressure liquid formamide UPS spectrum, which has already been reported, serves as an independent test of the accuracy of the present method. In agreement with a detailed investigation of experimental offset potentials, a measurement of the electrical current transported by the jet provides a highly accurate absolute calibration of the photoelectron spectra with respect to the vacuum zero energy level. The corrected spectra show several ionization bands which are shifted by approximately 1 eV to lower ionization energies with respect to the related gas phase molecular orbitals as a result of the electronic relaxation energy contribution to the molecular solvation forces. (C) 1998 Elsevier Science B.V. All rights reserved.