Stark-broadening study of neutral nitrogen lines

Abstract

Extensive photoelectric measurements of the plasma-broadened line shapes of 42 neutral nitrogen lines have been carried out with a wall-stabilized arc. The arc current was varied from 20 to 100 A to achieve a variation in the axial electron density from about 5 \ifmmode\times\else\texttimes\fi{} ${10}^{16}$ to 1.5 \ifmmode\times\else\texttimes\fi{} ${10}^{17}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. Most observations were made end-on, and the arc was operated in pure nitrogen as well as argon with a small admixture of nitrogen to avoid self-absorption problems, which mainly arose with the red and near-infrared lines. The electron density was determined from the well-known Stark half-width of the hydrogen ${H}_{\ensuremath{\beta}}$ line, for which purpose a trace of hydrogen was added to the plasma. Our principal results are as follows: (a) Good agreement with the recent theoretical work by Griem and co-workers has been obtained; (b) consistent with theoretical predictions, ion-broadening effects are not noticeable; (c) the Stark widths and shifts for different lines in a multiplet are identical within the experimental precision (\ensuremath{\cong} 3%) as predicted by the theory; and (d) measurements performed over a range of transitions involving different quantum states agree equally well with the theoretical data, indicating that the atomic-structure part of theory is very adequate.