Difiusion of Excited Neutral Particles: Basic Studies and Potential Applications⁄

Recent experiments, carried out in highly pure samples of molecular nitrogen, have demonstrated the strong in°uence exerted by neutral, excited metastable states. The in°uence of the electronically excited, metastable N2(A) state on the ionisation growth is demonstrated through observation of the difiusion phenomena associated with the spatial and temporal growth of ionisation. Evidence has also emerged demonstrating the existence of a second metastable particle in°uence. The difiusion time observed, however, is not consistent with it being due entirely to an electronically excited state such as the metastable N2(a 0) state. Rather the observations suggest the possibility that intersystem crossings between the N2(a 0), the highly vibrationally excited N2(X) states and the N2(A) state may be responsible for the increased difiusion time and large molecular size. The possible relevance of these flndings to applications such as plasma nitriding is canvassed. 1