We report the observation of intense continuous vacuum ultraviolet radiation in the range 60-100 nm from microhollow cathode discharge plasmas in high-pressure He (up to 600 Torr). Two prominent emissions, a narrow, sharply peaked feature in the region of 58-65 nm and a broad emission from 65 to 95 nm are attributed to the He*2 first- and second-excimer continuum emission, respectively. We also observed several narrow atomic emission lines in the 95-125-nm range that correspond to atomic O, N, and H emission lines. We attribute the presence of these atomic line emissions to near-resonant energy transfer processes involving the He*2 excimers and trace concentrations of the impurities O2, N2, and H2 in the discharge feed gas. The processes leading to the atomic line emissions in the present case are similar to the near-resonant energy transfer process observed previously in high-pressure microhollow cathode discharge plasmas in Ne/H2 gas mixtures, which resulted in the emission of intense, monochromatic atomic hydrogen Lyman-α radiation (P. Kurunczi et al. J. Phys. B: At. Mol. Opt. Phys. 32 (1999) L651). He*2 excimer formation in a microhollow cathode discharge plasma is initiated by low-energy electron collisions (excitation of the metastable He levels or ionization of the He atoms) followed by three-body collisions. The emission of He*2 excimer radiation from a microhollow cathode discharge plasma indicates that these discharges are very efficient sources of energetic electrons, as the formation of He*2 excimers requires a sufficiently large number of electrons with energies well above 20 eV.
- Energy-transfer processes
- High-pressure plasmas
- Hollow cathode discharges
- Low-energy electron collisions
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry