Infrared Spectroscopic and Kinetic Studies of Molecular Ions and Hydrogen in Glow Discharges with a Difference Frequency Laser System.

A difference frequency laser system has been used to study the fundamental molecular ions rm H_3^+, CH_3^+, C_2H_3^+, NH_2^+, O_2H^+, CH_5^+, and rm H_3O^+, and the H_2 molecule in positive column and hollow cathode glow discharges. The studies have been both infrared spectroscopic (2200-3600 cm ^{-1}) and kinetic in nature. It has been observed that using 100% parahydrogen instead of normal H_2 (75% ortho, 25% para) produced a nonthermal ortho-to-para ratio of H_3^+ in the plasma. This nonthermal distribution of nuclear spins also demonstrates that nuclear spin selection rules are obeyed in the chemical reactions within the plasma. To calculate this nonthermal H_3^+ distribution, the chemical reactions within the plasmas were investigated. A group theoretical method of counting nuclear spins was then formulated, which was incorporated into steady-state rate equations. High J, K spectral lines of H_3 ^+ and CH_3^+ have been assigned and their rotational temperatures in various plasmas were calculated. Extended assignments were also made for rm C_2H_3 ^+ and NH_2^+. In the hydrogen and hydrocarbon discharges, plasma chemical reactions were investigated to explain the population distribution of rovibrational levels of H_3^+ and CH_3^+ in the positive column discharge and the abundance and formation of rm C_2H_3^+ in the hollow cathode discharge. A search was made for the elusive molecular ions CH_5^+ and rm O_2H^+. Although the scans obtained did not yield their infrared spectra, new features were discovered in the 5g-4f Rydberg spectrum of H_2 , which was observed during the search for CH _5^+. These were the presence of hyperfine structure in orthohydrogen transitions and population inversion and stimulated emission in triplet higher vibrational levels. Plasma processes were also examined to explain the detection and production of these Rydberg states of H_2. Finally, an extended analysis of the nu_3 bands of rm H_3O ^+ was made, and Delta {mid}k-1{mid} = 3 transitions were observed. The latter enabled the calculation of the mixing coefficient tau_ {XXXZ} and the sum of the rotational constants (C-9D_{kk}).