Pre-breakdown discharges through isotopically enriched nitrogen: Possible contributions from highly vibrationally excited molecules

The spatial and temporal ionization growth of pre-breakdown discharges in N-14(2) is compared with that in N-15(2). The spatial growth of the ionization current shows differences which are attributable to differences in secondary-ionization processes caused by metastable-particle activity. The secondary processes are less efficient in N-15(2) than they are in N-14(2). This is consistent with a previous suggestion (Fewell et al 1996 Chem. Phys. 206 257-67) that diffusion not only of the first electronically excited state but also of highly vibrationally excited electronic ground states of the nitrogen molecule plays a significant role in pre-breakdown discharges through nitrogen.