ABSORPTION OSCILLATOR STRENGTHS FOR MOLECULAR NITROGEN

Abstract

Nitrogen has been cited from the time of the earliest spectroscopic investigations for its remarkable ability to store energy. One of the first observed manifestations of such energy retention was the appearance of the Lewis-Rayleigh afterglow which is well-established as arising from the recombination of nitrogen atoms produced in an electric discharge. The long-lived low-lying triplet states of $N_{2}, A^{3}\Sigma_{u}^{+}$ and the $W^{3}\Delta_{u}$, have received considerable attention as energy depositories and the $B^{\prime}$ $^{3}\Sigma_{u}^{-}$, although less subject to observation, undoubtedly plays a similar role in many environments. In the singlet manifold, the lower excited states of molecular nitrogen, $a^{^{\prime}1}\Sigma_{u}^{-}, a^{1}\Pi_{g},$ and $w^{1}\Delta_{u}$, are of interest as being relatively long lived, with the $a^{\prime}$ under consideration as a possible precursor in the formation of auroral NO. Quantitatively, the relatives significance of the roles of the above-mentioned states in participating in energy-transfer processes depends on the values of their radiative lifetimes and the associated oscillator strengths. We have made a series of measurements on the oscillator strength for transitions connecting such low-lying singlets and triplets with the ground state and we present our results to this point. For the $\nu = 0$ level of $a^{^{\prime}1}\Sigma_{u}^{-}$, the lowest excited singlet level of nitrogen, a life-time of 0.013 sec is obtained.