THRESHOLD PHOTOELECTRON-SPECTROSCOPY OF HBR AND DBR

The threshold photoelectron spectra of HBr and DBr have been recorded with varying resolution (3-20 meV) over a wide photon energy range (11 .5-31.5 eV) using synchrotron radiation and a penetrating-field electr on spectrometer, encompassing both the outer- and inner-valence ioniza tion regions. Extensive vibrational structure has been observed in the X((2)Pi(i)) band systems for both isotopomers in the Franck-Condon ga p region, between the X((2)Pi(i)) and A((2)Sigma(+)) states, that is a ttributed to the resonance autoionization of 5s sigma, 6s sigma and 7s sigma (1)Sigma(+) Rydberg states. Resonance autoionization is also fo und to play a role in the vibrational bands within the A((2)Sigma(+)) system that is associated with both non-predissociated and predissocia ted vibrational levels of the A((2)Sigma(+)) state. This is evident by the observed increased broadening of these vibrational bands in compa rison to those formed in conventional photoelectron spectroscopy obtai ned at a similar resolution. Photoionization of HBr and DBr in the inn er-valence ionization region between 23 and 29 eV shows four sets of p airs of very similar, vibrationally resolved band systems that are ide ntified as being due to satellite ion states and a single, vibrational ly resolved, band system assigned to the 'main-line' 4s sigma(-1) ioni zation. Absolute vibrational numbering in these systems was greatly fa cilitated by having the isotopomer threshold photoelectron spectra. Ev idence for the direct excitation of repulsive ion states in the 17.5-2 3.0 eV range has been found. (C) 1998 Elsevier Science B.V. All rights reserved.