H- production in hydrogen DC glow discharge

The H- ion dynamics in the positive column of H-2 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 similar to 40 Td up to similar to 170 Td. Using a partial modulation of the discharge current, it is shown that the H(-)concentration follows H atom dynamics due to a fast detachment reaction with the atoms; the higher the H density, the lower the H-/n(e) ratio. The dynamics of H atom density during discharge modulation was measured by time-resolved actinometry on Ar atoms, while H-2 vibrational temperature was estimated by comparing measured and simulated H-2 VUV absorption spectra. The analysis of the experimental dependencies of H- and H/H-2 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 discharge model, self-consistent state-to-state vibrational kinetics as well as H-2 highly excited electronic states were developed. The main processes that contribute to H- production and loss are discussed in detail. Dissociative attachment to vibrationally excited H-2(v) molecules is the main channel of H- production but occurs via the excitation of the well-known low-energy (& varepsilon;(th) approximate to 3 eV) shape resonance of H-2(-)(X-2 Sigma(+)(u)) only at low E/N. At high E/N, the H- production mostly occurs via the excitation of high-energy H-2(-) states, such as H-2(-)(B-2 Sigma(+)(g), A(2)Sigma(+)(g), C-2 Pi(u)) and Feshbach resonances similar to H-2(-)((2)Sigma(+)(g)) Rydberg state.