The third continuum of the rare gases emitted by heavy ion beam induced plasmas

Rare gases have been excited by dc ion beams of He+, Ne+ and Ar+ in the energy range 0.5–3.9 MeV using the Stuttgart DYNAMITRON accelerator and the gas target system RHINOCEROS. The VUV emission of the first, second and third continua was observed in the wavelength range between 50 and 300 nm. Especially the third continuum of neon could be observed at 99 nm for the first time in this way. The relative intensities of the continua depend strongly on the mass of the exciting ion and on the presence of contaminations. The observations support strongly the assignment of the third continuum to the radiative decay of Rg2+2 ionic excimers.