Population development of auroral molecular nitrogen species in a pulsed electric discharge

A series of experiments has been performed with pulsed electric discharges in low‐pressure nitrogen in order to elucidate excitation processes which underlie auroral photon emission. Flowing nitrogen in a large‐volume glass container at 30 to 3000 mtorr is excited by 4 µs pulses which, typically, are at 12000 V and 900 A. The radiation issuing from the discharge tube is analyzed by means of time‐resolved spectroscopy with particular attention given to the nitrogen first positive system, B³Πg → A³Σu+. Dramatic changes have been noted in the relative band intensities of the 1PG spectra subject to the influence of the variation of the experimental conditions. In particular, the distribution of population among vibrational levels of the B³Πg state evolves in time both during and after the exciting electric pulse, with the trends strongly correlated with the numbers of collisions. Further, radiation from these excited vibrational levels continues at much higher emission rates than those commensurate with their radiative lifetimes. Both of these observations constitute evidence of the intersystem collisional transfer of excitation. The distinguishing feature of this array of experiments is the application of time‐resolved spectroscopy which permits examination of the development of level populations on a collision‐by‐collision basis.