Electron impact dissociation of ND+: formation of D+

Abstract

Nitrogen is a common contaminant species in fusion reactors such as the ITER (International Thermonuclear Experimental Reactor). Thus, the collisional properties of nitrogen-containing plasma compounds arewidely studiedexperimentally andtheoretically. Here we show the results of absolute cross section measurements for the electron impact dissociative excitation of ND+ yielding D+, especially at low electron energies near the onset of the dissociation. The identification of indirect and resonant processes is a particular challenge in that energy regime. Excitation is likely to be influenced by vibrationally excited levels populated within the X2Π ground state of ND+(v). Twomechanisms can produce these levels: (i) the endothermic reaction D2 +(v’) + N and (ii) the ion–molecule reaction D2(v”) + N+. The latter is the first step in a sequence ofmolecular activated processes, which confirms that such a reaction chain is important for an understanding of the overall plasma chemistry. The low experimental energy threshold observed in the present studies indicates that the importanceof contributionofRydberg states via the capture of the incoming electron into doubly excited electronic states of (ND)**.