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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.

The interaction of volatile species with carbonaceous interstellar dust analogues is of relevance in the chemistry and physics of dense clouds in the interstellar medium. Two deposits of hydrogenated amorphous carbon (HAC), with different morphologies and aromatic versus aliphatic ratio in their structure, have been grown to model interstellar dust. The interaction of N2, CO, CH4, and CO2 with these two surfaces has been investigated using thermal programmed desorption (TPD). Desorption energy distributions were obtained by analysing TPD spectra for one monolayer coverage with the Polanyi–Wigner equation. The desorption energies found in this work for N2, CO, and CH4 are larger by 10–20 per cent than those reported in the literature for siliceous or amorphous solid water surfaces. Moreover, the experiments suggest that the interaction of the volatiles with the aromatic substructure of HAC is stronger than that with the aliphatic part. Desorption of CO2 from the HAC surfaces follows zero-order kinetics, reflecting the predominance of CO2–CO2 interactions. A model simulation of the heating of cold cloud cores shows that the volatiles considered in this work would desorb sequentially from carbonaceous dust surfaces with desorption times ranging from hundreds to tens of thousands of years, depending on the molecule and on the mass of the core. [ABSTRACT FROM AUTHOR]

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.

We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41-49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution. The impedance matching of the cell windows has been studied using different materials. The choice of the material and its thickness was critical to obtain a sensitivity identical to that of standard radio astronomical observations. Spectroscopic signals arising from very low partial pressures of CH3OH, CH3CH2OH, HCOOH, OCS, CS, SO2 (<10-3 mbar) were detected in a few seconds. Fast data acquisition was achieved allowing for kinetic measurements in fragmentation experiments using electron impact or UV irradiation. Time evolution of chemical reactions involving OCS, O2 and CS2 was also observed demonstrating that reactive species, such as CS, can be maintained with high abundance in the gas phase during these experiments. [ABSTRACT FROM AUTHOR]

Context. Ice mantles that formed on top of dust grains are photoprocessed by the secondary ultraviolet (UV) field in cold and dense molecular clouds. UV photons induce photochemistry and desorption of ice molecules. Experimental simulations dedicated to ice analogs under astrophysically relevant conditions are needed to understand these processes. Aims. We present UV-irradiation experiments of a pure CO2 ice analog. Calibration of the quadrupole mass spectrometer allowed us to quantify the photodesorption of molecules to the gas phase. This information was added to the data provided by the Fourier transform infrared spectrometer on the solid phase to obtain a complete quantitative study of the UV photoprocessing of an ice analog. Methods. Experimental simulations were performed in an ultra-high vacuum chamber. Ice samples were deposited onto an infrared transparent window at 8K and were subsequently irradiated with a microwave-discharged hydrogen flow lamp. After irradiation, ice samples were warmed up until complete sublimation was attained. Results. Photolysis of CO2 molecules initiates a network of photon-induced chemical reactions leading to the formation of CO, CO3, O2, and O3. During irradiation, photon-induced desorption of CO and, to a lesser extent, O2 and CO2 took place through a process called indirect desorption induced by electronic transitions, with maximum photodesorption yields (Ypd) of ∼1.2 × 10-2 molecules incident photon-1, ∼9.3 × 10-4 molecules incident photon-1, and ∼1.1 × 10-4 molecules incident photon-1, respectively. Conclusions. Calibration of mass spectrometers allows a direct quantification of photodesorption yields instead of the indirect values that were obtained from infrared spectra in most previous works. Supplementary information provided by infrared spectroscopy leads to a complete quantification, and therefore a better understanding, of the processes taking place in UV-irradiated ice mantles. [ABSTRACT FROM AUTHOR]

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 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.