H– production in hydrogen DC glow discharge.

H- ion dynamics in the positive column of H2 dc glow discharge was studied by the laser photodetachment technique in a wide range of pressure, 0.1–3 Torr, and current, 1-30 mA which cover a range of E/N from ~ 40 Td up to ~ 170 Td. Using partial modulation of discharge current it is shown that the H– concentration follows H atom dynamics due to fast detachment reaction with the atoms: the higher H density, the lower H-/ne ratio. Dynamics of H atom density at discharge modulation was measured by the time-resolved actinometry on Ar atoms while H2vibrational temperature was estimated by comparing measured and simulated H2 VUV absorption spectra. The analysis of the experimental dependencies of H– and H/H2 on the discharge parameters allowed estimating the effective rate constant of H– production in the discharge as a function of the reduced electric field. For this the discharge model including self-consistently state-to-state vibrational kinetics as well as H2 highly excited electronic states was developed. The main processes, that contribute to H– production and loss, are discussed in detail. Dissociative attachment to vibrationally excited H2(v) molecules is the main channel of H- production but occurs via the excitation of the well-known low-energy (εth ≈ 3 eV) shape resonance of H2-(X2Σu+) only at low E/N. At high E/N, the H- production mostly occurs via the excitation of the high-energy H2- states, such as H2-(B2Σg+, A2Σg+, C2Πu) and Feshbach resonances similar to H2-(2Σg+) Rydberg state.