Abstract

The nonequilibrium conditions common to plasma media are revealed dramatically in a N₂ gaseous discharge by different rotational and vibrational temperatures. The rotational temperature (T_R) characterizes the local gas temperature through the usual strong coupling between the rotational and translational motions of the molecules. The vibrational temperature (T_V) results from the coupling of the low-energy electrons (typically in the 2-3-eV range) with the nitrogen molecules. This coupling involves the transient formation of ${\text{N}}_2^{-}$ which, upon de-excitation, leaves the molecule in an excited vibrational state. Because of the homopolar configuration of the molecule, de-excitation by dipolar radiation is forbidden, which added to the relatively low collision rates present at low pressures (10-40 Torr) and modest temperatures (500- 800 K), allows the vibrational populations to greatly exceed that allowed by the local gas translational temperature.

© 1991 Optical Society of America