Cation-like Doppler shifts from a neutral molecule in an electrical discharge

Abstract

Velocity-modulation Fourier transform emission spectra from a N 2 O/He discharge plasma recorded between 1 and 5.5 µm are described. Surprisingly, they show Doppler-shifted lines for the E 2 Σ + -D 2 Σ + , C 2 Π-A 2 Σ + , and D 2 Σ + -A 2 Σ + Rydberg-Rydberg rovibronic transitions of the nitric oxide neutral molecule. These polarity-dependent Doppler-shifts are those of positively charged particles. Vibration-rotation lines of NO and transitions from other neutral molecules like N 2 are also present in the spectra with comparable intensities and remain unshifted. Experimental investigations and possible explanations are discussed.