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

Velocity-modulation Fourier transform emission spectra from a N2O/He discharge plasma recorded between 1 and 5.5 μm are described. Surprisingly, they show Doppler-shifted lines for the E2Σ+–D2Σ+, C2Π–A2Σ+, and D2Σ+–A2Σ+ 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 N2 are also present in the spectra with comparable intensities and remain unshifted. Experimental investigations and possible explanations are discussed.