Rare Gas Mixtures Research Articles

Microwave and rf excitation of a discharge in sulfur vapor with added neon

An experimental investigation was made of the transient emission of a discharge excited by microwave radiation in mixtures of sulfur and rare gases. Several typical spectral types of emission were identified which alternate over time.

Formation of ArCl(B) molecules in a transverse volume discharge

Results of optimizing a λ=175 nm ArCl(B-X) emitter pumped by a transverse volume discharge are presented. The formation of ArCl(B) molecules was investigated in a plasma formed by mixtures of rare gases with HCl and Cl2 molecules. It is shown that the Cl2 molecule is the most efficient chlorine carrier and that neon at pressures ≥ 50 kPa is the most efficient buffer gas.

Methodology for gas chromatographic–mass spectral analysis of volatile organic compounds emerging from a low-pressure, flow-through reaction cell

A methodology has been developed for the analysis of volatile organic compounds (VOCs) emerging from a plasma discharge cell operating at a constant flow-rate under subatmospheric pressure (0.266 to 2.66 kPa). The analytical system consisted of a gas reservoir for trapping a portion of the VOC–rare gas mixture, a sampling loop for cryogenically concentrating the VOC products, and either gas chromatography–mass spectrometry (GC–MS) or gas chromatography–flame ionization detection (GC–FID). The methodology was evaluated for the analysis of methylene chloride, benzene and tetrachloroethylene, using n-octane as the internal standard. Calibration curves were constructed by plotting the pressure ratios of the gas standard relative to the internal standard versus the corresponding peak area ratios. Over a pressure range of 1.133 to 5.32 kPa, the linearity of the calibration curve for each gas standard was determined with correlation coefficients ranging from 0.96 to 0.98. The relative standard deviation for a minimum of triplicate analyses varied from 1.1 to 18.3% for most VOCs. The calibration curves were used to measure the concentration of premixed VOC–rare gas mixtures as a function of energy input of the plasma reactor.

Investigation of a -discharge plasma under an increased pressure of Ar and in narrow tubes

The electrokinetic characteristics (the electron energy distribution function, the strength of the longitudinal electric field and the concentration and average energy of electrons) are measured and calculated in a -discharge plasma under a high pressure of argon (up to 30 Torr) and in narrow tubes (the tube radius is less than 1.0 cm). A simple method of treating the second derivative of the probe current with respect to the probe potential is proposed for a straightforward way to obtain the electron energy distribution function under a high pressure of a gas. It is shown that the main assumptions on which modelling of the plasma of mercury luminescent lamps is based are also valid for the plasma in question. This leads to the existence of special similarity laws and gives a new possibility for diagnostics based on the similarity properties of the plasma. The approach proposed in the work can be easily extended to the mixtures of mercury vapour and other rare gases.

Excimer emission spectra of rare gas mixtures using either a supersonic expansion or a heavy-ion-beam excitation

Results related to the energy transfer in the rare gas mixtures are reported for an electrical discharge excitation with plasma expansion and a heavy-ion-beam excitation. Energy transfer from the lighter rare gases to the heavier ones was observed in a very efficient way for both excitation mechanisms. Strong emission from excited atomic states, which are possible candidates for new lasers, was observed for the electrical discharge case. The broad-band emission of the discharge sources makes them appropriate for strong lamps in the VUV. Some comparisons of the two excitation mechanisms were discussed with respect to the energy deposition, the density of dimers and their vibrational relaxation.

Ultraviolet induced mechanisms in oxide film formation

Relatively intense ultraviolet light can be generated using dielectric barrier discharges to form excimer mixtures of rare gases and rare-gas halides. The characteristics of the emission spectra of the excimers formed, from 126 to above 308 nm are found to be useful for thin film and surface processing. The underlying operating mechanisms of these sources, whose conversion efficiencies (from input electrical to output optical energy) can be as high as 15%, under optimum conditions, are described. These low cost, high power, large area excimer systems can provide an interesting and potentially very useful alternative to conventional Hg as discharge UV lamps for industrial large-scale UV processes. Their application towards oxide grown on silicon, and a range of other processes, is described.

A vacuum ultraviolet flash lamp with extremely broadened emission spectra

We have developed a vacuum ultraviolet (VUV) flash lamp using a binary rare gas mixture excited by a pulsed silent discharge. In a Kr/Xe silent discharge, the VUV emission spectral width was extended up to 26 nm full width at half-maximum (FWHM) at a center wavelength of 162 nm. According to kinetic analyses, such a spectral extension in mixed rare gases is attributed to the simultaneous emissions from heteronuclear rare gas excimers (KrXe*) and homonuclear rare gas excimers (Kr2* and Xe2*).

Anomalous light-induced drift of potassium in Ne plus rare-gas mixtures

We report anomalous light-induced drift of potassium vapor in mixtures of Ne with another rare gas. The drift velocity versus laser frequency curve shows a strong deviation from the dispersion curve predicted by the standard theory of light-induced drift based on velocity-independent collision rates. The observed drift velocity versus frequency curves have three zero-crossings. For a qualitative explanation of the results, a strong collision model with velocity-dependent collision rates is used. The partial pressures that cancel normal light-induced drift also provide accurate ratios of cross section for potassium collisions with the various buffer gases. The observation of anomalous light-induced drift in a simple atomic system offers the opportunity to relate the results to potential curves. \textcopyright{} 1996 The American Physical Society.

The analog of Blanc’s law for drift velocities of electrons in gas mixtures in weakly ionized plasma

The analog of Blanc’s law for drift velocities of electrons in multicomponent gas mixtures in weakly ionized spatially homogeneous low-temperature plasma is derived. The obtained approximate-analytical expressions are valid for average electron energy in the 1–5 eV range typical for plasma conditions of low-pressure direct current (DC) discharges. The accuracy of these formulas is ±5%. The analytical criterion of the negative differential conductivity (NDC) of electrons in binary mixtures of gases is obtained. NDC of electrons is predicted in He:Kr and He:Xe rare gas mixtures.

Persistent spectral hole burning in dye-doped quench condensed argon-xenon matrices

We report the extension of our studies on dye-matrix interactions in simple model systems from pure rare-gas hosts to solid matrices of rare-gas mixtures Ar 1 − x xe x , doped with the dye molecule free-base phthalocyanine. In our experiments we determined the respective solvent shifts and inhomogeneous widths of the Q x -bands as well as the quasihomogeneous line widths from hole-burning experiments. While the solvent shifts show a gradual transition between the values in pure rare gas matrices with varying mixing ratio, the widths of the Q x -absorption bands are constant over the measured range. The homogeneous line widths show no significant increase as compared to the pure rare gas matrices. This is at first surprising, since the structural differences (nanocrystalline in pure rare gas matrices as compared to amorphous structure in mixtures) were expected to have a much greater impact on the line widths.

Excitation of vacuum ultraviolet transitions in a discharge of rare-gas mixtures with alkali-metal vapours

Collisional energy transfer of excited rare-gas atoms with alkali-metal atoms was studied in a gas discharge of their mixtures by monitoring the vacuum ultraviolet (VUV) line intensities and by a comparison with the approximate solutions of the rate equations. The method used enabled us to obtain depletion cross sections of rare-gas atom resonance states by alkali-metal atoms in a discharge of their mixtures for the following atom pairs: He* by Rb sigma d=8.8*10-15 cm2, Ne* by Rb sigma d=2.0*10-16 cm2 and Ar* by Cs sigma d=1.2*10-15 cm2. The fundamental processes of atomic collisions producing alkali-metal quartet quasimetastable highly excited states in a discharge plasma were studied. The cross section of Rb(4p55s5p)4S32/ quasimetastable excitation in non-elastic collisions with neon metastable atoms was measured to be 2.0(+or-0.8)*10-15 cm2. The quasiresonant charge transfer from a caesium ion metastable to a caesium atom produces Cs(5p55d6s)4P52/ quasimetastable states with a cross section of 9(+or-3)*10-15 cm2. These reactions lead to quasimetastable level population in the discharge, which is important for applications in VUV laser schemes.

Collison-induced absorption by H2-He pairs in the H2 fundamental band at 78 and 298 K.

Measurements of collision-induced absorption spectra in the H[sub 2] fundamental band are reported for gaseous mixtures of hydrogen and helium at temperatures of 78 and 298 K and frequencies from about 3900 to 5200 cm[sup [minus]1]. Spectral line shapes are calculated from the fundamental theory with the isotropic interaction approximation, which has been successful in all previous comparisons of the kind for pure hydrogen and hydrogen--rare-gas mixtures. In the present case, however, the comparison of measured and calculated absorption profiles suggests that small differences between theory and measurement may exist for H[sub 2-]He in the H[sub 2] fundamental band, which are marginaly greater than the combined uncertainties of theory and measurement. Presumably, these are due to the neglect of the anisotropy of the interaction; the H[sub 2]-He system in the H[sub 2] fundamental band is more sensitive to the anisotropy of the interaction than the systems and bands studied previously.

Investigation of rare gas–oxygen exciplexes

Mixtures of rare gases (Rg) with oxygen donors at high pressures were excited by an electron beam. The fluorescence spectra in the ultraviolet were investigated. Besides the well-known continua of KrO (180 nm) and XeO (235 nm) several new transitions were identified. They are attributed to the decay of RgO and possibly of Rg2O. The study of the reaction kinetics yielded the rate constants for the most important buildup and decay reactions of KrO and ArO. The inverse lifetime of KrO was determined to be 3 × 106 s−1 for ArO to be <3 × 106 s−1.

Diffusion and Quenching of Metastable Xe Atoms in Mixtures of Xe and Rare Gases

The diffusion coefficient of metastable Xe*(6s[3/2]2o) atoms has been measured in mixtures of Xe with rare gases. Experimental values ranging from 5.5× 1017 cm-1s-1 in pure Xe to 6.1× 1018 cm-1s-1 in pure He are compared with those obtained from the gas kinetic theory using Lennard-Jones potential parameters. Quenching rate coefficients of Xe* for two-body and three-body collisions with rare-gas atoms have also been determined.

New possible laser media in the UV and XUY in high current heavy ion beam induced plasmas

Mixtures of rare gases with alkali-metal vapour were excited by a high power argon ion beam in a windowless gas target system. Narrow emission continua were observed in the vacuum ultraviolet region between 60 and 200 nm. The observed emission was assigned to the decay of a new class of excited ionic molecules Rg+ A formed by the combination of a rare gas ion Rg+ with an alkali atom A. These excimer-like ions are of great interest for possible short-wavelength lasers, because the ground state consisting of a rare gas atom and an alkali ion is only weakly bound. The observed decay energies and fine structure splittings agree well with the prediction of calculations. A summary of previous results is presented.

Fluorescence des gaz rares à haute pression excités par flash X rapide

In this work, we report on flash X-ray excitation of high pressure pure rare gases (He, Ne, Ar, Kr, and Xe) and mixture of rare gases. It is shown that high efficiency in energy deposition could be achieved using this new excitation means. Such an energetic excitation leads to important population of highly excited ionic species. As a consequence, the fluorescence emitted from the rare gases is mainly located in the UV-VUV wavelength domain. The high level of fluorescence observed authorized time resolved spectroscopy using conventional means. The dominant feature of the spectra appears to be the second and third continua of rare gases. The use of this specific technics of excitation leads to an efficient production of heteronuclear ions at high pressure.

The commensurate-incommensurate phase transitions in monolayers of physisorbed mixtures of rare gases: a simple model

Two-dimensional hexagonal crystals of mixtures of rare gases, without vacancies and at zero 2D-pressure, were generated (using mostly Lennard-Jones (LJ) interactions); vibrations were taken into account only through effective temperature-dependent parameters. The calculation of the mean lattice parameter shows clearly a “swelling” due to the local (chemical) disorder, which is reflected as an enhancement of the energy. The effect of differences in atomic diameters and interactions is discussed and in particular the role of anharmonicity is emphasised. Anharmonicity also has a great effect on the interatomic distances between the various types of atomic pairs. It is shown that pairs of argon (but not of krypton) in xenon are almost dissociated.For the study of physisorption on surfaces such as graphite we add a periodic potential. Consideration of the ideal entropy of mixing allows for the study of transitions between commensurate and incommensurate phases (ICT): their limits of coexistence at 45 K are compared (for different depths of modulation of the adsorption potential) to experimental results for the case of physisorption of Ar-Xe and Kr-Xe on graphite.

Electron Transport in Helium-Rare-Gas Mixtures

New calculations of electron transport in helium-rare-gas mixtures are presented. It is shown that the elastic collisions with helium in helium Ramsauer rare gas mixtures play analogous roles to weak inelastic collisions in molecular gas Ramsauer rare gas mixtures. The results illustrate that the swarm analyses of helium Ramsauer rare gas mixtures provide unique momentum transfer cross sections for the Ramsauer rare gases at low electron energies. The results significantly impact the low energy inelastic cross sections of molecular gases derived from swarm measurements.

Infrared spectroscopy of low-temperature matrix-isolated chlorofluoroamine radicals

NFCl radicals were isolated in low-temperature argon, krypton, and xenon matrices. The matrices were produced by passing the NFCl 2 /rare gas mixture through a stainless steel metering valve and depositing the effluent from the valve onto a cold (10 H) HCl window. Infrared spectra of the matrices were measured, and absorbances at 720 and 917 cm -1 were assigned to the N-Cl and N-F stretches of NFCl, respectively. The N-Cl peak was split into two peaks, with a 3:1 ratio as expected for the 35 Cl and 37 Cl isotopic components. The normal-coordinate analysis for NFCl is also reported

Observation of collision-induced amplified emission in Na-noble gas system

A stimulated resonance emission and stimulated Raman scattering signals have been generated in an atomic sodium and rare gas mixture by a laser tuned to the 32 S1/2-32 P3/2 transition. The intensity dependence of these effects on the buffer gas pressures is obtained in the experiment.