Vibrational distributions of the A 2Πu state of CO+2 and CS+2 produced by electron impact on jet-cooled CO2 and CS2

Fluorescence spectra of the Ã2Πu–X̃2Πg system of CO+2 and CS+2 ions, following electron impact on supersonic jet targets of CO2 and CS2, have been analyzed to determine vibrational populations. The vibrational distributions of the Ã2Πu state of CO+2 and CS+2 were found to be independent of the impact energy in the 30–300 eV range. The distribution of the CO+2(Ã) state is very similar to the result obtained by He i photoelectron spectroscopy (PES), which is a Franck–Condon-type vertical ionization, whereas that of the CS+2(Ã) state is significantly different from the PES data. This non-Franck–Condon behavior for formation of CS+2(Ã) in the electron impact is discussed.