Velocity modulated Fourier transform emission as a plasma diagnostic and a spectroscopic tool

Abstract

The Doppler shifts of the emissions from the A–X and B–X transitions of N+2 ions in a He glow discharge are measured using the method of Fourier transform emission (FTE) spectroscopy. The magnitudes and pressure dependencies of the Doppler shifts of rovibronic lines of the two electronic transitions are distinctly different mainly due to the difference in the lifetimes of the excited states. By fitting the data to a theoretical model, the cross sections for He–N+2 collisions (both for velocity-changing and quenching collisions) are obtained. The data from the short-lived B 2Σ+u state of N+2 in the low pressure (no-collision) regime lead to the determination of the discharge electric field. The Doppler modulated spectra demonstrate that the FTE method is a useful spectroscopic tool for discriminating between ionic and neutral transitions.