THRESHOLD PHOTOELECTRON-SPECTROSCOPY OF CL-2 AND BR-2 UP TO 35 EV

We have investigated the threshold photoelectron spectra of Cl-2 and Br-2 over the energy range from the onset of ionization up to 35 eV, using synchrotron radiation and employing a penetrating-field electron spectrometer. The near-zero kinetic energy electron spectra in the valence ionization region reveal resolved vibrational structure in the direct formation of all valence ionization states. In addition, extended vibrational structure is found in the Franck-Condon gap region between the X (2) Pi(g,i) and A (2) Pi(u,i) systems that is indicative of the presence of autoionizing states. Analysis of the vibrational structure contained in these band systems has generated improved spectroscopic constants. Extensive vibrational structure in the A (2) Pi(u,i) band system of Br-2(+) has been observed from both direct ionization and autoionization processes, enabling us to define the band origin of the lower spin-orbit component. Energy perturbations are found in the lower vibrational bands (nu' = 0-7) in the Br-2(+)(A (2) Pi(u,3/2)) subsystem. In the higher energy region studied, band structures related to core ion and satellite ion state formation have been found in both halogen systems.