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We have studied laboratory low pressure (0.1 mbar ≤ p ≤2 mbar) glow air discharges by optical emission spectroscopy to discuss several spectroscopic techniques that could be implemented by field spectrographs, depending on the available spectral resolution, to experimentally quantify the gas temperature associated to transient luminous events (TLEs) occurring at different altitudes including blue jets, giant blue jets, and sprites. Laboratory air plasmas have been analyzed from the near UV (300 nm) to the near IR (1060 nm) with high (up to 0.01 nm) and low (2 nm) spectral resolution commercial grating spectrographs and by an in‐house intensified CCD grating spectrograph that we have recently developed for TLE spectral diagnostic surveys with ≃0.45 nm spectral resolution. We discuss the results of lab tests and comment on the convenience of using one or another technique for rotational (gas) temperature determination depending on the altitude and available spectral resolution. Moreover, we compare available low resolution (3 nm ≤Δλ≤7 nm) N21PG field recorded sprite spectra at 53 km (≃1 mbar), and resulting vibrational distribution function, with 1 mbar laboratory glow discharge spectrum (Δλ=2 nm) and synthetic sprite spectra from models. We found that while the relative population of N2(B3Πg,v=2−7) in sprites and laboratory produced air glow plasmas are similar, the N2(B3Πg,v=1) vibrational level in sprites is more efficiently populated (in agreement with model predictions) than in laboratory air glow plasmas at similar pressures. Rotational (gas) temperature determination due to TLEsBest techniques to gas temperature estimation in TLEsComparison of TLE and laboratory air spectra

Low‐pressure, plasma‐enhanced (PE)CVD is a powerful and versatile technique that has been used for thin‐film deposition and surface treatment since the early 1960s. However, it is only recently that it has been used in applications other than the different stages of microelectronic circuit fabrication. Now, PECVD is being used in emerging applications due to new materials and process requirements in a wide variety of areas, such as biomedical applications, solar cells, fuel cell development, fusion research, or the synthesis of silicon nanocrystals showing efficient photoluminescence, useful for future solid‐state light sources. These new scenarios have stimulated further development of novel PECVD diagnostic techniques, together with fundamental experimental and theoretical studies aimed at a better understanding of some of the basic processes underlying the plasma/surface interaction. This paper gives an overview of some new research areas where PECVD is finding promising applications.

The well-known radical and ion scavenger techniques of application in amorphous hydrogenated carbon film deposition studies are investigated in relation to the mechanism of tritium and deuterium co-deposition in carbon-dominated fusion devices. A particularly successful scheme results from the injection of nitrogen into methane/hydrogen plasmas for conditions close to those prevailing in the divertor region of present fusion devices. A complete suppression of the a-C : H film deposition has been achieved for N₂/CH₄ ratios close to one in methane (5&percent;)/hydrogen DC plasma. The implications of these findings in the tritium retention control in future fusion reactors are addressed.

Gas phase compounds produced in low pressure dc hollow cathode flowing discharges of acetylene, dimethylsulfide (DMS) and dimethyldisulfide (DMDS) have been, by the first time, identified and quantitatively measured through in situ FT-IR absorption spectroscopy. Experimental discharge parameters have been varied in the ranges where stable enough plasmas were produced. A high conversion of precursors to non-volatile compounds is observed. Only diacetylene has been detected in the infrared spectra of acetylene/inert gas discharges, with yields between 3 and 13%. Its appearance indicates that the C 2 H radical is the main intermediate species produced in such discharges. CS 2 , CH 4 and C 2 H 2 have been the most abundant products detected in the infrared spectra of DMS and DMDS plasmas, their maximal yields being in the range 5-20%. The concurrent production of CO, CO 2 and OCS, with yields one to two orders of magnitude lower, must be attributed to oxidation processes of the precursors due to air traces in the discharge cell. No final gaseous compounds, either oxygenated or not, suggesting the production of the CH 3 S radical as intermediate species were detected in these plasmas. The results presented clearly prove that hollow cathode discharges (HCD) produce cold plasmas where high temperature chemistry is conducted.

The rotational relaxation of nitrogen molecules in collisions with neon has been studied in supersonic expansions. N2 rotational temperatures have been determined from resonance-enhanced-multiphoton-ionization (REMPI) spectra performed in a series of supersonic molecular beams of N2 diluted in Ne. Terminal flow velocities and translational temperatures for the two expansion partners have been obtained from mass-selected time-of-flight measurements. From the measured data, the approximate isentropic behavior of the expansion could be verified and the thermal cross section for N2/Ne rotational relaxation at very low temperatures could be derived. The cross section increases from a value of ≈35 Ų at 5 K, goes through a maximum of about 55 Ų between 10 and 20 K, and then decreases smoothly to ≈25 Ų for T = 60 K. The relaxation cross section for N2/Ne collisions is larger than that for N2/N2 collisions below roughly 20 K and smaller above this temperature.

The dynamics of the gas-phase reaction of H atoms with HCl has been studied experimentally employing the laser photolysis/vacuum-UV laser-induced fluorescence (LP/VUV-LIF) “pump-and-probe” technique and theoretically by means of quasiclassical trajectory (QCT) calculations performed on two versions of the new potential energy surface of Bian and Werner [Bian, W.; Werner, H.-J. J. Chem. Phys. 2000, 112, 220]. In the experimental studies translationally energetic H atoms with average collision energies of Ecol = 1.4 and 1.7 eV were generated by pulsed laser photolysis of H2S and HBr at 222 nm, respectively. Ground-state Cl(²P3/2) and spin−orbit excited Cl*(²P1/2) atoms produced in the reactive collision of the H atoms with room-temperature HCl were detected under single collision conditions by VUV-LIF. The measurements of the Cl* formation spin−orbit branching ratio φCl*(1.4 eV) = [Cl*]/[Cl + Cl*] = 0.07 ± 0.01 and φCl*(1.7 eV) = 0.19 ± 0.02 revealed the increasing importance of the nonadiabatic reaction channel H + HCl → H2 + Cl* with increasing collision energy. To allow for comparison with the QCT calculations, total absolute reaction cross sections for chlorine atom formation, σR(1.4 eV) = (0.35 ± 0.16) Ų and σR(1.7 eV) = (0.13 ± 0.06) Ų, have been measured using a photolytic calibration method. In addition, further QCT calculations have been carried out for the H + DCl isotope reaction which can be compared with the results of previous reaction dynamics experiments of Barclay et al. [Barclay, V. J.; Collings, B. A.; Polanyi, J. C.; Wang, J. H. J. Phys. Chem. 1991, 95, 2921].

In this work the changes in the infrared absorption of N2O observed in a hollow cathode discharge modulated by a 45 Hz square wave are studied by time-resolved infrared absorption spectroscopy, with a Fourier transform infrared (FTIR) spectrometer working in the step-scan mode. These variations are attributed to alternative population and depopulation of the ground state of N2O; on the other hand, no changes are observed in the total concentration of N2O and the major products of the discharge. The experimental results are explained by means of a simple kinetic model:  vibrational excitation processes are assumed to be the main cause of the observed effects, but an inhomogeneous distribution of the stable species and the incorporation of diffusion terms between the plasma volume and the rest of the discharge cell are shown to be crucial in order to justify the quick and sharp variations in the N2O ground-state population seen along the path of the IR beam. The influence of these effects has been verified also 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.

The present work describes the first experimental study of the transients involved in the turn on and off of a N2O hollow cathode discharge until the attainment of the respective stationary states. Time-resolved Fourier transform infrared spectroscopy and quadrupole mass spectrometry with ionization by electronic impact have been used to measure the temporal evolution of the concentrations of the stable species present in the discharge N2O, N2, O2, NO, and NO2. A model based on a reduced set of kinetic equations gives a global account of the measured data; this model takes into account all the mechanisms considered in a former work (Arcos, T. et al. J. Phys. Chem. A 1998, 102, 6282) to explain the steady state of a continuous N2O discharge but includes also additional mechanisms to which transient phenomena have proven to be much more sensitive than the stationary results. In particular, excitation of some vibrational levels of N2O and homogeneous reactions of vibrationally excited species, as well as electron impact dissociation of the stable products of the discharge are considered. On the other hand, the partial formation of NO2 by an heterogeneous reaction previously proposed seems to be confirmed.

The rotational relaxation of molecular nitrogen has been investigated down to temperatures of about 5 K with a combination of resonance-enhanced multiphoton ionization and supersonic beam time-of-flight techniques. The average rotational relaxation cross section obtained shows a maximum value of 50−60 Ų at 20−30 K. For lower temperatures this cross section decreases and reaches a value smaller than 30 Ų at T ≈ 5 K. For temperatures above 30 K, the cross section decreases slowly as the temperature grows and converges approximately to the determinations from other non-jet techniques and theoretical estimates available for T > 80 K. The results are compared to previous measurements from other groups using different methods, and general good agreement is found. However, we observe a significant discrepancy with some of the data from electron-beam-induced fluorescence that yield much larger cross sections for temperatures lower than 30 K.

The quasiclassical trajectory method has been applied to the calculation of cross sections and rate constants for the H + D2 → HD +D reaction on three ab initio potential energy surfaces. The results include state-selected cross sections for the reaction with D2(v=0,j=0−9) and D2(v=1,j=0) and thermal rate constants in the 200−1500 K temperature range. A global good agreement is found between the present results and those from experiment and from approximate quantum mechanical calculations. This agreement is particularly good between 200 and 900 K. At higher temperatures, the quasiclassical rate constants deviate gradually toward lower values. A detailed comparison is performed between the reactivity of this isotopic variant and that of D + H2. Special attention is paid to the effect of rotational excitation on reactivity, which is opposite for the two isotopomers, and to the microscopic dynamics responsible for the observed ratio of thermal rate constants and cross sections. In particular, the larger reaction cross section of D + H2 as compared with H + D2 is found to be caused by the more efficient transfer of collision energy from the heavier D atom to the molecular bond of the lighter H2 molecule. These findings can be rationalized with simple dynamical models.

A new, compact atomic beam source based on the supersonic expansion of He has been developed for application as a plasma edge diagnostic. The beam is produced from a pulsed valve with a duration between 0.2 to 2 ms and a nominal repetition rate < 500 Hz . A terminal speed ratio > 10 and a divergence of ± 1° have been achieved at stagnation pressures below 2 bar. The diagnostic has been tested in ECRH plasmas on the TJ-IU torsatron, representing the first application of a supersonic beam to plasma characterization, to our knowledge. Operational conditions which minimized the total amount of He injected into the plasma were chosen. Non-perturbative injection conditions in the low density plasmas could be obtained at local He densities of ⋍ 1 × 10 cm and a beam diameter < 1 cm . Due to the relatively low electron density of the ECRH plasmas, and to the good penetration characteristics of the supersonic He beam, the diagnostic could be used up to fairly low values of the normalized plasma minor radius, r a (a = 12 cm) . Details of the optimization of the atomic beam diagnostics and typical results for steady state conditions in the TJ-IU plasmas are presented.

The present work describes a systematic experimental investigation of a N2O hollow cathode discharge. The local electron mean energy and density have been determined with a double Langmuir probe. Fourier transform infrared spectroscopy and mass spectrometry have been employed for the measurement of the concentration of the stable species present in the discharge. N2O, N2, O2, and NO are always identified as the main constituents of the discharge plasma. In addition, NO2 is found for the first time in a glow discharge of nitrous oxide. As a plausible explanation, a reaction of NO with oxygen atoms adsorbed on the cathode walls is proposed, although homogeneous reactions of vibrationally excited species cannot be discarded. A model based on a reduced set of kinetic equations including electron dissociation, gas-phase reactions, and gas−surface processes can give a global account of the measured data for all the experimental conditions used. The results are discussed and, when possible, compared to previous works on other types of N2O glow discharges.

The relaxation of the energy stored in the translational and rotational degrees of freedom of N2 and CH4 in the course of free jet expansions has been experimentally studied. Rotational temperatures along the expansion axis were obtained by means of stimulated Raman spectroscopy, and terminal flow velocities and translational temperatures were determined from supersonic beam time-of-flight measurements. From these measurements low-temperature cross sections for rotational relaxation have been estimated. The results are compared with data from other experiments, and the validity of simple relaxation models is discussed.