Dynamics of the formation of excited hydrogen,H(n=2,3,4), during a pulse discharge in methane

The dynamics of the formation and decay of excited hydrogen during a pulse discharge in methane at a pressure of 200 Pa and energy density of 0.05 J/cm³ has been studied. The population of hydrogen in the n=2 state was monitored by the laser absorption method. The time constant of the decay of the excited hydrogen was measured to be 95±15 ns. The concentration of free electrons reached a maximum value of 7×10¹⁴ cm^–3, and the time constant of their recombination was 220±50 ns. The formation of appreciable amounts of atomic hydrogen in the ground state during the discharge, H(n=1)>10¹⁶ cm^–3, was estimated on the basis of a kinetic model.Notation absorption coefficient - wave number, cm^–1 - c velocity of light - e electron charge - m_e mass of electron - A_mn Einstein coefficient - F_mn collisional deexcitation rate constant - S_m ionization rate constant - f₂₄ oscillator strength - n_e electron concentration - n_H(n=2,3,4) excited-state hydrogen concentration - v_e electron velocity - q_mn excitation cross-section - (q_mnve) excitation rate constants - T_e electron temperature - E (t) electrical field strength - j current density - t_ei^–1 electron-ion collision frequency - _2,m two-body recombination rate constant - _3,m three-body recombination rate constant