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The chemical composition of low-pressure hydrogen dc plasma produced in a hollow cathode discharge is measured and calculated. The concentrations of H atoms and of H(super +), H(sub 2)(super +) and H(sub 3)(super +) ions are determined with a combination of optical spectroscopic and mass spectroscopic methods and the results are rationalized with the help of a zero-order kinetic model.

The low-temperature rotational relaxation of CO in self-collisions and in collisions with the rare-gas atoms Ne and He is investigated using spectroscopy and time-of-flight techniques. The results show some discrepancies found between the present relaxation cross sections for CO-CO and CO-He and the values derived from the electron-induced fluorescence experiments.

The dynamics of the gas-phase reaction of H atoms with HCI was investigated experimentally by employing the laser photolysis/vacuum-UV laser-induced fluorescence(LP/VUV-LIF) pump and probe technique. The experimental studies stated that the translationally energetic H atoms with average collision energies of E(sub col)=1.4 and 1.7 eV were generated by pulsed laser photolysis of H(sub 2)S and HBr at 222 nm.

A study is conducted to examine the changes in the infrared absorption of N2O observed in a hollow cathode discharge modulated by a 45 Hz square wave. The influence of the effects is verified by mass spectrometric measurements of the temporal behavior of the concentration of the major products N2O, N2 and O2 at one end of the discharge cell and at different frequencies.

Mass spectrometry is used for determining the distributions of ions and neutrals in low-pressure DC discharges of pure hydrogen and hydrogen with small admixtures of C[H.sub.4] and [N.sub.2]. The results have shown that very little HCN is formed in the plasmas.

The neutral and charged species present in a direct current (dc) hollow cathode, gas flow, air reactor are experimentally studied by quadrupole mass spectrometry. A kinetic model of the plasma including electrons, neutrals, and positive ions is developed to predict that heterogeneous processes are the main source of NO and that the contribution of ions to the global chemistry of neutrals is of minor significance even for the lowest pressures.

A study of the rotational relaxation of N2 in collisions with NE over a similar temperature range (5-60K) in supersonic expansions, which include also the transition to the adiabatic regime for rotational energy transfer, is presented. The results show that the translational equilibrium between two mixture components is maintained over most of the range and hints of separation appear just for the lowest Knudsen number expansions.

An investigation of the transient processes which occur around the ignition and extinction of a low frequency, square wave modulated, hollow cathode discharge of N2O until the attainment of the respective stationary states is presented. There is good agreement between the model predictions and the experimental data for the N2O, N2, O2 and NO.

A study was conducted to analyze the rotational relaxation of molecular nitrogen with a combination of resonance-enhanced multiphoton ionization and supersonic beam time-of-flight methods. Free jets of pure nitrogen were generated by expanding the gas from a solenoid-driven pulsed valve. The final velocity distributions of molecular beams were then determined. Moreover, two different skimmers were used in the measurements.

A study was conducted to characterize a N2O hollow cathode discharge. A double Langmuir probe was utilized to obtain the local electron mean energy and density. The concentration of the species present in the discharge was determined using Fourier transform infrared spectroscopy and mass spectrometry. Experimental results indicated that nitric oxide contributes was less than 10% of the total number density.

The ionic polymerization of acetylene in cold plasmas of C 2 H 2 /He and C 2 H 2 /Ar has been experimentally studied and modeled in radio frequency (rf) discharges with conditions selected to avoid particle formation. Steady-state distributions of positive and negative ions were measured with mass spectrometry. All the measured distributions are dominated by ions with an even number of carbon atoms, reflecting the characteristic polyyne structures typical for the polymerization of acetylene. The distributions show a monotonic decrease in intensity from ions with two carbon atoms until the highest number of atoms detected. For cations, the distributions extend until 12 carbon atoms. The anion distributions extend further, and negative ions with 20 C atoms are observed in the C 2 H 2 /Ar plasma. From the measured mass spectra it is not possible to decide on the possible presence of aromatic species in ions with more than six carbon atoms. A simple model assuming a homogeneous discharge was used to describe the plasma kinetics and could account for the measured ion distributions with reasonable values of charge density and electron temperature. The results of this work stress the important role of the vinylidene anion and indicate that Ar and He do not have much influence on the carbon chemistry.