  A long life-time (>0.3 ms) strongly-coupled molecular Rydberg plasma is generated by the excitation of nitric oxide into the high-n Rydberg threshold region in the high-density region of a supersonic jet expansion. After 310 \mus the plasma has expanded to a size of ca. 3 cm. When subjected to very small DC fields from 0.2 to 1.0 V/cm the plasma reveals a much smaller high-density core structure of only 0.6 cm. The molecular Rydberg plasma is observed over a broad range of excitation energies, from threshold down to Rydberg states as low as n = 19. 
Some properties of a long lifetime strongly-coupled molecular plasma   produced by high Rydberg excitation of nitric oxide in a supersonic free jet