  Velocity-modulation Fourier transform emission spectra from a N_2O/He
discharge plasma recorded between 1 and 5.5 $\mu$m are described. Surprisingly,
they show Doppler-shifted lines for the E ^2 \Sigma ^+ - D ^2 \Sigma ^+, C ^2
\Pi - A ^2 \Sigma ^+, and D ^2 \Sigma ^+ - A ^2 \Sigma ^+ 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.
