The cathode-fall of low-pressure hydrogen discharges: Absolute spectral emission and model

Absolute excitation probabilities from very low to moderate-current hydrogen discharges in parallel-plane geometry are measured and used to test models. Relative emission data are obtained for the Hα line, the H2 (a3Σ → b3Π) near-UV continuum, and the H2 (G1Σ→B1Πu+) band at pressures of 0.5 and 2 Torr, a 1.05 cm gap, and voltages from 300 to 900 V. Electron behavior is traced using the first negative (A2Σg → X2Πu, ν″ = 0 → ν′ = 0) band of N2+ by adding 2% N2. Relative measurements of Hα, H2 near-UV, and N2 1st negative emission are placed on a absolute scale by normalization to published measurements and Boltzmann calculations of electron excitation. Emission probabilities calculated using a multi-beam kinetics model for the electrons, H+, H2+, H3+, H−, H, and H2 are compared with the calibrated experiments. Fast H atoms are calculated to produce Hα excitation that is comparable with that of electrons. The calculated emission intensities for Hα and H2 near-UV continuum are within a factor of three of the ...