Dissociative Recombination of Xe 2 + and XeH+

Abstract

When excited in a plasma, xenon has useful emissions in the visible and ultraviolet. Indeed, its visible spectrum resembles closely the solar spectrum making it very attractive as an illumination light source. Xenon is used in discharge lamps, lasers and in plasma display devices. Being inert, it is nontoxic and therefore represents an attractive replacement for mercury in fluorescent lamps. Given this interest in its spectral response, it is not surprising therefore, that there have been many spectroscopic studies of xenon. During one such study, the authors came upon an unusual phenomenon that owes its existence to associative ionization and dissociative recombination processes. The recombination rates of homonuclear rare gas dimers (with the exception of He 2 + ) are large due to the fact that they have suitably placed curve crossings that allow the capture of an electron by the ion to be followed rapidly by dissociation along a neutral state. This dissociation process results in the conversion of potential energy into kinetic energy, and thus, the potential energy of the electron plus ion system drops below the ionization potential, rendering re-ionization impossible. The free atoms resulting from this dissociative recombination process can be formed in a variety of different energy levels, and information on the branching ratios for the formation of these states is very important for the modeling of the light emission from plasmas containing such molecular ions.