Supersonic cooling of rare-gas excimers excited in dc discharges

Emission spectra of the homonuclear rare-gas excimers have been investigated in the wavelength region of 50 to 200 nm by using continuous discharges with supersonic jet expansion. The well-known dimer bands were readily observed in the emission spectra of He, Ar, Kr, and Xe along with an extremely weak band of Ne. A detailed examination of the Ar(2) band at 128 nm was carried out, and its envelope and bandwidth (8.7 nm) indicate significant vibrational cooling owing to supersonic expansion.