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The interest in the production of nanoparticles (NPs) within Ar/C2H2 reactive plasmas is increasing, driven by their potential applications in functional materials or for their analogy to cosmic dust. The growth process of NPs has been thoroughly examined using a broad array of diagnostic tools. Significant among these tools are those that determine two-dimensional distributions of NP sizes and densities. The inherent complexity of these techniques has resulted in a limited number of works that integrate these measurements with a multitude of other diagnostic tools. Here, we show a multi-diagnostic exploration of the growing process of NPs in Ar/C2H2 plasmas. The combination of in-situ techniques, such as scattered light images, optical emission spectroscopy, light extinction, quadrupole mass signals, or self-bias voltage, with ex-situ scanning electron microscopy images and FTIR spectra of the deposited dust, provides a detailed picture of the growth process. The temporal evolution of plasma parameters, coupled with chemical composition measurements, provides a comprehensive description of the dust growth phases, and the FTIR measurements reveal an appreciable difference in chemical composition between the core and shell of the NPs. Furthermore, employing a method based on the terminal falling velocity of NPs in the afterglow, the intrinsic mass density of NPs is estimated. The asymmetries observed in the spatial distributions of NP size and density are qualitatively discussed in terms of neutral drag, ion drag, and electrostatic forces. [ABSTRACT FROM AUTHOR]

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.

A quadropole mass spectrometer and the threshold ionization technique were used to determine the presence of neutral CH3 radicals in a hollow cathode discharge cell containing methane. The results showed that CH3 production efficiency was greater than that observed in other modes of discharges. However, CH4 density significantly decreased and the mass spectrum of the discharge indicated that compounds appeared after the recombination process.

Integral cross sections and thermal rate constants have been calculated for the N(2D)+H2 reaction and its isotopic variants N(2D)+D2 and the two-channel N(2D)+HD by means of quasiclassical trajectory and statistical quantum-mechanical model methods on the latest ab initio potential-energy surface [T.-S. Ho et al., J. Chem. Phys. 119, 3063 (2003)]. The effect of rotational excitation of the diatom on the dynamics of these reactions has been investigated and interesting discrepancies between the classical and statistical model calculations have been found. Whereas a net effect of reagent rotation on reactivity is always observed in the classical calculations, only a very slight effect is observed in the case of the asymmetric N(2D)+HD reaction for the statistical quantum-mechanical method. The thermal rate constants calculated on this Potential-Energy Surface using quasiclassical trajectory and statistical model methods are in good agreement with the experimental determinations, although the latter are somewhat larger. A reevaluation of the collinear barrier of the potential surface used in the present study seems timely. Further theoretical and experimental studies are needed for a full understanding of the dynamics of the title reaction. [ABSTRACT FROM AUTHOR]

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]

In this work several lines of the ν3 fundamental band of the CH3 radical have been detected in a refrigerated hollow cathode discharge multipass cell filled with CH4, by using a discharge and laser amplitude double modulation technique, with a difference frequency laser spectrometer and a double phase sensitive detection. Bands of the precursor CH4 and of C2H4 and C2H6 produced in the discharge have been observed too. By Doppler broadening and absorption variations, the increase of temperature with the establishment of the discharge has been tested. It is only ∼15 °C. Nevertheless, a very high sensitivity in transmittance variations with temperature is achieved for transitions from highly excited levels of stable species. The method proposed can be very useful for the assignment of very weak bands. [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]