Observation of long-lived nitrogen afterglow following low-pressure theta-pinch discharges

A pulsed theta-pinch discharge was generated in low-pressure nitrogen and nitrogen–oxygen mixtures. Here, we report multisecond postdischarge emission at a total pressure of 1.44 Pa and a discharge voltage of 11 kV. In pure \(\hbox {N}_{2}\) , the yellow–green afterglow persisted for approximately 18 s and decreased monotonically without measurable chromatic variation. Time-resolved spectroscopy showed that the visible emission was dominated by the \(\hbox {N}_{2}\) first positive system, \(B^{3}\Pi _g\rightarrow A^{3}\Sigma _u^+\) , with \(v'=12\) and \(v'=11\) exhibiting the largest relative upper-state vibrational populations, supporting its identification as a Lewis–Rayleigh-type afterglow. Additional O I emission and NO \(\gamma \) system bands were observed in the nitrogen–oxygen mixture. The slow characteristic decay time decreased from 5.86 s in pure nitrogen to 3.04 s in the mixture containing 79% \(\hbox {N}_{2}\) and 21% \(\hbox {O}_{2}\) , demonstrating oxygen-induced acceleration of the decay under low-pressure conditions. In contrast, a kinetic estimate gives a nitrogen-atom lifetime of only approximately 2.1 ms in atmospheric air, showing that the low-pressure result cannot be directly extrapolated to atmospheric conditions. Selected spectral features partially overlap with those reported for the 2012 Qinghai Plateau ball-lightning event, but this non-unique similarity does not establish a common mechanism. The results provide laboratory constraints for a testable working hypothesis involving nitrogen recombination in a transient oxygen-depleted and/or reduced-density region.