Knowledge Bank

We have undertaken a series of investigations to attain an understanding of the role of collisions in the determination of the relative populations of the excited states of molecular nitrogen in electric discharges. Earlier, we had noted that emission originates in vibrational levels of these electronic states which would be populated only very sparsely through the agency of direct electron excitation from the ground state. Furthermore, the influence of collisions is underscored by the observed differences between $N2$ emission spectra in the aurora and in the $laboratory.1$ We have found many cases among the neighboring vibrational levels of the $W\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}△u,B\prime \mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma u-$ and $B\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma g$ states where the populations are completely equilibrated by collisions in laboratory discharges down at least as far as the 100 milliTorr pressure range. This circumstance provides a powerful tool for quantitative spectroscopic analysis in that in a number of situations we have been able to infer unknown level populations from their collisional equilibration with known level populations.