Excited states in the radiation chemistry of gaseous diatomic hydrides

Although some uncertainty concerning the yield of triplet excited states exists, the yields of ions and atoms predicted from electron impact cross-sections and other information are in relatively good agreement with experimental data for the radiolysis of H₂. A substantial contribution to the atom yield comes from excited states lying just below and above the ionization potential. Less information is available for hydrogen halides. However, while rapid auto-ionization occurs for some superexcited states of HCl, there is again evidence for disscoiations- in this case to form H(1s) and excited Cl. The occurence of this type of process is supported by energy balance calculations for both HCl and HBr. The behaviour of the low-lying excited states of these molecules is relatively well understood.