Pumping of highly vibrationally excited molecules in a hydrogen flow through a cesium-hydrogen discharge

Abstract

There is a considerable interest in the creation of vibrationally excited molecules because of their application to ion volume-plasma sources, plasma chemistry etc. It has been shown that a low-voltage discharge in a Cs- mixture might be used as an effective source of vibrationally excited molecules. In this paper it is shown that the vibrational distribution function (VDF) of molecules may be significantly improved if vibrational excitation occurs in a moving flux of molecules penetrating through the discharge. The following theoretical model is considered. Hydrogen flux flows in a flat channel and passes successively through two sections. Section I is a discharge section, where low-voltage Cs- discharge occurs and vibrationally excited molecules are created. In section II, the excited hydrogen flows in a plane channel, with cold walls. Because of the large value of the mean vibrational energy of a molecule, a significant intensification of the high vibrational level population takes place in section II. This intensification is of the order of - for several vibrational levels. The increase of the vibrational level population occurs due to the diffusion of vibrational quanta, by v-v exchange, up to high vibrational levels. The VDF, obtained at the exit of section II, is significantly improved for the purposes of generation by means of dissociative attachment.