Hydrogen Lyman-α and Lyman-β emissions from high-pressure microhollow cathode discharges in Ne-H₂ mixtures

We observed intense emission of the atomic hydrogen Lyman-α (121.6 nm) and Lyman-β (102.5 nm) lines from microhollow cathode discharges in high-pressure Ne (740 Torr) with a small admixture of H₂(up to 3 Torr). The atomic emission lines are spectrally clean with essentially no background of molecular emissions from the H₂ Lyman and Werner bands. We attribute these atomic emissions to near-resonant energy transfer processes in the high-pressure discharge. In one case, near-resonant energy transfer between the Ne₂^* excimer and H₂ leads to the formation of H(n = 2) atoms, a process similar to what was observed recently by Wieser et al (1998 J. Phys. B: At. Mol. Opt. Phys. 31 4589) in a high-pressure Ne/H₂ mixture excited by energetic ion and electron impact. In the other case, near-resonant energy transfer between excited Ne^* atoms (or vibrationally excited neon excimer molecules) and H₂ leads to the formation of H(n = 3) atoms. The ratio of Lyman-α to Lyman-β emission intensity depends on the operating parameters of the discharge (gas pressure, gas mixture, discharge current) which supports the notion that different processes are involved in the formation of the H(n = 2) and H(n = 3) atoms, respectively.