Threshold photoelectron spectroscopy of HF in the inner valence ionizationregion

The threshold photoelectron (TPE) spectrum of hydrogen fluoride has been re corded using synchrotron radiation and a penetrating-field electron spectro meter over the photon energy range 30-52 eV encompassing the inner valence ionization region. The TPE spectrum is characterized by a dominant, broad b and system and a weaker broad band system both of which are assigned to the 'main line' for (2s sigma)(-1) ionization, with some vibrational structure evident on the more intense one of these. The results of this study contra st with the findings for the TPE spectra of the inner valence ionization re gion of the heavier halogen acids and this is explained on the basis of dif ferences between potential energy curves for the dicationic states. Observa tion of a broad, structureless band system on the low energy side of the 'm ain-line' band systems is attributed to indirect autoionization of neutral Rydberg states. (C) 1999 Elsevier Science B.V. All rights reserved.