Phelps AV. Energetic ion, atom, and molecule reactions and excitation in low-current H2 discharges: model.
PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009;
79:066401. [PMID:
19658606 DOI:
10.1103/physreve.79.066401]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2009] [Indexed: 05/28/2023]
Abstract
Models of the elastic, inelastic, and reactive collisions of energetic hydrogen ions, atoms, and molecules are developed for predicting H_{alpha} and H2 near-uv emission, H_{alpha} Doppler profiles, and ion energy distributions for low-pressure, low-current discharges in H2 . The model is applied to spatially uniform electric field E to gas density N ratios of 350 Td< or =E/N< or =45 kTd and 8 x10;{19}< or =Nd< or =10 x10;{21} m;{-2} , where d is the electrode separation and 1 Td=10;{-21} V m;{2} . Mean ion energies at the cathode are 5-1500 eV. Cross sections for H+ , H2+ , H3+ , H, H2 , and excited H(n=3) collisions with H2 and reflection probabilities from electrodes are updated and summarized. Spatial and energy distributions of ions and fast neutrals are calculated using a "multibeam" technique. At the lower E/N and Nd , electron excitation of H_{alpha} dominates near the anode. Excitation of H_{alpha} by fast H atoms near the cathode increases rapidly with pressure through a multistep reaction sequence. At higher E/N , fast H atoms produced at the cathode surface excite much of the H_{alpha} . The model agrees with experimental spatial distributions of H_{alpha} emission and Doppler profiles. Ion energy distributions agree with experiments only for H2+ . Cross sections are derived for excitation of the near-uv continuum of H2 by H atoms.
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