PENNING IONIZATION ELECTRON SPECTROMETRY OF HYDROGEN IODIDE

The energy spectra of electrons released in thermal energy ionizing co llisions of metastable helium and neon atoms with hydrogen iodide have been measured with high resolution and low background. The electron s pectra, obtained for a mixed He(2(1)S, 2(3)S) beam, a pure He(2(3)S) b eam, and a mixed Ne(3s P-3(2), P-3(0) beam, are all characterized by t he formation of the X2PI(i) and A 2SIGMA+ states of HI+. For both He(2 (1)S) + HI and He(2(3)S) + HI the spectra exhibit some broad features in the medium electron energy range which are attributed to ionization from an additional charge exchanged potential surface (He+ + HI-) in the entrance channel. For the first time, we have detected the low ene rgy electrons in the He(2(1)S, 2(3)S) spectra due to autoionization of I* atoms which result from energy transfer to highly excited, dissoc iative HI* Rydberg states. The HI+ (X) 2PI3/2:2PI1/2 fine-structure b ranching ratIos vary significantly with the ionizing agent in a simila r way as for the isoelectronic, atomic target case xenon.