N2 Kr Research Articles

Cluster growth in binary N2–Kr supersonic jets: Effect of initial gas temperature and krypton gas concentration

An electron diffraction diagnostics of substrate-free clusters formed in N2–Kr binary jets expanding through a supersonic nozzle into a vacuum was carried out. Gas mixtures contained 0.5, 1, and 6 mol % krypton, the measured average sizes of aggregations in the cluster beam varied from 500 to 30000 molecules per cluster. A change in the nucleation mechanism in the jet from homogeneous to heterogeneous was revealed when the temperature of the gas mixture at the nozzle inlet T0 decreased from 120 to 100 K, which had a profound effect on the sizes, phase composition, and component composition of the clusters. The effect of cluster growth suppression by adding impurity with stronger intermolecular forces was revealed for the first time. It is shown that the effect is caused by the kinetics of gas condensation in a supersonic jet and is manifested at T0 = 120 K when the krypton gas content increases to 6 mol %. It was established that the intensification of cluster growth by inserted krypton nucleation centers at T0 = 100 K occurs through an increase in the fraction of the fcc phase compared to the hcp.

Investigations of the properties of filaments generated in gas mixtures pumped by femtosecond laser pulses

In this paper, we compare the properties of filaments generated in a Ne–N2 mixture, pure N2, a Kr–N2 mixture, and a Xe–N2 mixture pumped by femtosecond laser pulses systematically. Due to different nonlinear refractive indices and ionization potentials of these noble gases, the clamped intensity and plasma density can be tuned in a certain range when small amounts of different noble gases are injected into pure N2. In addition, we also demonstrate that a higher proportion of noble gas and shorter incident pulse duration can have the benefit of manipulating the plasma density on a relatively larger scale.

Structural transformations in N2–Kr alloys

The structural characteristics of N2–Kr alloys were studied using electron diffraction over the entire range of mutual concentrations. The samples were prepared in situ by condensing a gaseous mixture on aluminum and carbon substrates at temperatures of 5 and 20 K. The structure and solubility regions of the solutions were determined. The maximum solubility values of the components were: less than 20 mol.% for krypton in a nitrogen crystal, and less than 11 mol.%. for nitrogen in solid krypton. Phase separation of the solid solution was observed in a concentration range of 20–89 mol.% Kr. The effect of diluting the molecular matrix with krypton on the orientational ordering of N2 molecules in the solutions was investigated. An experimental dependence of the orientation order parameter on the solution composition was determined for N2-based solutions.The structural characteristics of N2–Kr alloys were studied using electron diffraction over the entire range of mutual concentrations. The samples were prepared in situ by condensing a gaseous mixture on aluminum and carbon substrates at temperatures of 5 and 20 K. The structure and solubility regions of the solutions were determined. The maximum solubility values of the components were: less than 20 mol.% for krypton in a nitrogen crystal, and less than 11 mol.%. for nitrogen in solid krypton. Phase separation of the solid solution was observed in a concentration range of 20–89 mol.% Kr. The effect of diluting the molecular matrix with krypton on the orientational ordering of N2 molecules in the solutions was investigated. An experimental dependence of the orientation order parameter on the solution composition was determined for N2-based solutions.

The Influence of Molecular Gas on the Apokamp Discharge Formation

Emission spectra of apokamp discharge plasma jets in CO2, Ar, Kr, N2, and their mixtures have been studied. It has been shown that the emission spectra of the Kr–N2 mixture contain N2 and $$\rm{N_2^+}$$ bands, as well as Kr lines. The spectrum of the Ar–CO2 mixture is presented by bands of the Fox–Duffendack–Barker system and lines of the exited argon atom. In all gas media under study, the reduction of the molecular gas quantity leads to the transition from an apokampic discharge in the form of a diffusion jet developing from the current channel to a volume discharge with a strong transverse glowing. The experimental apparatus described in this work is proposed for use in laboratory investigations of spectral characteristics of transient luminous events observed in atmospheres of planets of the Solar System.

Cluster approach to formation of nitrogen–rare gas cryoalloys

The structure of solid binary N2–Kr and N2–Ar solutions was studied by transmission electron diffraction (THEED). The samples were prepared in situ by deposition of a gaseous mixture onto an Al substrate cooled to 20 K. The lattice parameters for low concentrations of one of the components were measured. The relative change of the lattice parameter per unit concentration is determined for N2 impurity in Kr and Ar, as well as for Kr and Ar in N2. Analysis of the concentration dependence of the lattice parameters for low fractions of both components was performed within a cluster model in the three-particle approximation.

Adsorption Equilibria of Krypton, Xenon, Nitrogen and Their Mixtures on Molecular Sieve 5A and Activated Charcoal

The adsorption equilibria of Kr, Xe and N2, which are constituents of the off-gas from nuclear reprocessing processes, on representative adsorbents (Molecular Sieve 5A (MS5A) and activated charcoal) were studied. Adsorption experiments were conducted in the temperature range of 77 to 323 K using a packed bed column. The adsorption isotherms for the activated charcoal adsorbent were successfully correlated by the vacancy-solution model. The adsorption isotherms for the MS5A adsorbent were properly correlated by the Langmuir model and the vacancy solution model. The adsorption experiments for the binary component systems (Kr—Xe, Kr—N2 systems) were also performed, and the results suggest that the coexistence of Xe greatly inhibits the adsorption of Kr. The coexistence of large amounts of N2 was also found to inhibit the adsorption of Kr. The experimental results for the adsorption equilibrium of binary component systems on the activated charcoal adsorbent were well reproduced by the vacancy solution model without parameter fitting. The binary adsorption equilibrium on the MS5A adsorbent is rather well predicted by the ideal adsorbed solution model without parameter fitting. The use of the vacancy solution model for this adsorption system requires the optimization of parameters, but the binary adsorption equilibrium is well reproduced with the optimized parameters.

Exchange-Coulomb potential energy surfaces, and related physical properties, for KrN2

Abstract The construction of exchange-Coulomb (XC) potential energy models for closed shell atom-closed shell molecule interactions, based on earlier work for rare gas-rare gas interactions, is discussed with explicit application to the KrN2 interaction. The construction of the new XC potential energy surface for KrN2 is based on recent results for the Heitler-London interaction energy, the long range dispersion energies, and the microwave spectra for this dimer. The adjustable parameters in the final XC potential are determined by fitting experimental second virial coefficients (all within experimental error), as a function of temperature, and three lines of the microwave spectra. With no further adjustment of parameters the resulting potential yields excellent predictions for all the frequencies of all the microwave transitions studied experimentally for seven isotopomers of KrN2, and good agreement with experiment for the binary diffusion, the interaction viscosity, and the mixture viscosity coefficients of KrN2 and for the cross sections associated with depolarized light scattering and nuclear spin relaxation for the KrN2 system. The agreement with experiment for the latter five properties is as good as can be expected from our scaled Mason-Monchick/infinite order sudden calculations for these properties. The final XC2 potential is apparently the most reliable potential to date for the KrN2 interaction and provides a very suitable starting point for further studies of the KrN2 system; the flexibility still inherent in the potential can be used, as required, for this purpose.

N2–Kr interaction: A multiproperty analysis

An earlier anisotropic N2–Kr potential energy surface [Chem. Phys. Lett. 88, 197 (1982)] of Lennard-Jones form, obtained by inversion of molecular beam differential scattering data, has been found to provide calculated transport–relaxation phenomena in good agreement with experiment, but leads to calculated second interaction virial coefficients which are significantly too low, and does not provide adequate agreement with recent microwave van der Waals spectral data. A modification of this surface to include a recent ab initio determination of the C6 dispersion coefficient, and to bring in the virial and microwave data, gives a new potential surface that is in good agreement with all available experimental data.

Classical trajectories on simple model potentials for N2–Kr: Comparison with relaxation and other data

We compare the ability of six N2–Kr potential energy surfaces to predict experimental interaction second virial coefficients, diffusion coefficients, mixture viscosity, thermal conductivity, and nuclear magnetic resonance (NMR) rotational relaxation cross sections. These include a previously published empirical surface derived from fits to molecular beam experiments and various model potentials of the Tang and Toennies (TT) type. The TT type potentials differ in the set of dispersion coefficients employed. Two sets are obtained from published ab initio calculations, another from combining rules and one from empirical considerations. The repulsive parameters have been obtained from published results of a charge overlap combining rule. A variation of the TT model suggested by Aziz is also used to further investigate the effect of the repulsive wall anisotropy on the rotational relaxation cross sections. Forty-five effective cross sections that determine the bulk transport and relaxation phenomena have been calculated by classical trajectories for temperatures ranging from 100 to 800 K. The sensitivity of the NMR-derived cross sections to the various characteristics of the anisotropy of the potential (such as the anisotropy in the well depth, in the high repulsive wall, in the low repulsive wall, and at V=0) are examined. The empirical anisotropic LJ(12,6) surface of Rotzoll provides the best agreement with the diffusion, viscosity, thermal conductivity, and NMR relaxation experimental results.

The microwave rotational spectrum of the van der Waals complex Kr–N2

Pure rotational transitions in the vibrational ground state of the van der Waals complex Kr–N2 have been measured using a cavity microwave Fourier transform spectrometer. For the isotopomers 84Kr–14N2, 86Kr–14N2, 84Kr–15N2, 86Kr–15N2, 82Kr–15N2, and 83Kr–15N2 a-type transitions with Ka=0 and 1 have been measured, confirming a C2v symmetry of the complex. A value for the 14N nuclear quadrupole coupling constant in free nitrogen 14N2 has been estimated from an analysis of the nuclear hyperfine structure in complexes of 14N2. 15N spin–rotation hyperfine structure could be observed and analyzed in the 21,2–11,1 and 21,1–11,0 rotational transitions of 84Kr–15N2. Rotational transitions of 83Kr–15N2 showed a nuclear hyperfine splitting due to 83Kr with nuclear spin 9/2 which has been attributed to the weak bonding with 15N2. For 84Kr–14N15N and 86Kr–14N15N, only transitions involving energy levels with Ka=0 have been found.

1 5N spin-relaxation studies of N2 in buffer gases. Cross sections for molecular reorientation and rotational energy transfer

Nuclear spin-lattice relaxation times (T1) have been measured as a function of temperature for 15N in N2 gas and in CH4, O2, CO, Ar, HCl, CF4, Kr, and Xe. The relaxation is dominated by the spin-rotation mechanism so that empirical values of the cross sections for rotational angular momentum transfer (σJ) are obtained as a function of temperature. The values of σJ/Å2 at 300 K are 13.6±0.4 (N2–CH4), 14.9±0.4 (N2–N2), 14.7±0.6 (N2–O2), 15.0±0.9 (N2–CO), 15.9±0.8 (N2–Ar), 22.7±0.6 (N2–HCl), 30±1 (N2–CF4), 18.1±0.5 (N2–Kr), and 19.8±0.5 (N2–Xe). For almost all cases, the temperature dependence of the cross section deviates from T−1.

Pore size evaluation for fine porous freeze‐dried cellulose acetate membrane by gas separation

AbstractThe pore size for a fine porous freeze‐dried cellulose acetate membrane was evaluated by gas separation methods, where the Present–deBethune equation was applied. Separation coefficients were referred to the calculated value for each pore size from this equation. Nuclepore, Millipore VS, and Millipore VC, whose pore sizes were already known by bubble point method, were tested for this method. Pore diameters for this cellulose acetate membrane, thus determined, were about 25 and 40 Å from Ar–Kr and N2–Kr separation systems, respectively, which agreed well with the results from electron microscope (50 Å) and N2 gas permeability (50 Å). However, it is impossible to apply this method to He gas separation, since He gas permeability is higher than the expected value as Knudsen flow, which indicates that some channels are existing in this membrane, where He gas is more permeable than the other gases.

Preparation of NbN by reactive magnetron sputtering using Ne and Kr inert diluents

Previous studies of the preparation of NbN by reactive sputtering have employed Ar–N2 gas mixtures. We have shown that high‐Tc films (Tc=14.2 K) can be prepared on substrates held near room temperature by sputtering a Nb target in a dc s‐gun magnetron with that gas mix. This paper reports the results of an investigation of the properties of NbN films sputtered in the same system using alternative inert gas diluents, specifically Ne and Kr. The Tc of these films was found to depend systematically on the N2 partial pressure, total gas pressure, and dc cathode voltage; the maximum transition temperatures obtained using Ne–N2 and Kr–N2 mixtures were 12.8 and 12.7 K, respectively. When Tc is plotted versus ρ a rough general correlation is observed, though data for films sputtered in each inert gas tend to segregate. We conclude empirically that sputtering NbN in an Ar–N2 ambient gives the highest film quality and that using Ne or Kr in place of Ar offers no advantages.

Mixed gases separation by fine porous freeze‐dried cellulose acetate membrane

AbstractA Freeze‐dried cellulose acetate membrane with high permeability and high separation factor was prepared. In the successive membrance process, the heat treatment temperature was 80°C for constant period of 10 min, acetone evaporation time was between 4 and 6 min, and the membrane was fixed during drying to prevent shrinkage. Gas permeabilities for such a membrane were inversely proportional to the square root of molecular weight, suggesting that the mechanism of gas flow through this membrane was Knudsen flow. Separation factors for H2He, ArKr, N2Kr, HeNe, H2Ne, HeAr, ArH2, HeKr, ArHe, and HeH2 were measured. These factors were higher than those of membranes reported already. Separation efficiency largely depended upon the combination of mixed gases. The combination of two atom molecules and one atom molecule lowered the separation efficiency compared with the combination of one atom molecule and one atom molecule.

Viscosity of the Binary Gaseous Mixtures of Nitrogen with Argon and Krypton

This paper presents new measurements of the viscosity of the binary mixtures N2–Ar and N2–Kr both at zero density and in the temperature range 25–500°C. The measurements are compared with extensive calculations based on the extended law of corresponding states proposed by Kestin, Ro, and Wakeham. It is found that the calculations represent all data with a standard deviation of 0.33% and a maximum deviation of less than 0.5%. This is taken as new and additional evidence for the validity of the law of corresponding states. The latter is used as a device for the interpolation and extrapolation of the data in the form of tables ranging from 0°C to 2000°C for the mole fractions 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 for each system.

Wavelength and relative intensity of the ultraviolet forbidden atomic nitrogen doublet

Absolute integral cross sections for collisions of N2 molecules and N atoms with Kr are measured as a function of velocity at thermal energies. For the N2Kr case the glory structure observed in the plot of cross section versus velocity is only slightly affected by the anisotropy of the interaction. An analysis in terms of a spherically averaged potential model can be performed, thus obtaining a reliable potential function. For the NKr system the occurrence of a well developed glory oscillation indicates low anisotropy in the interaction. An analysis in terms of a simple, realistic potential model has been performed to give potential parameters for the NKr system.

Thermal conductivity and eucken type correction for binary mixtures of N2 with some rare gases

The thick-wire variant of the hot-wire method has been used to measure the thermal conductivity of the binary mixtures N2He, N2Ne, N2Kr and N2Xe at 30°C and 45°C. The experimental data for pure N2 and the binary mixtures have been compared with the recent theory of Hirschfelder. Reasons have been put forward for the discrepancy observed between the experimental and the calculated values of the thermal conductivity of pure N2 given by the Hirschfelder's theory. The formula for the thermal conductivity of gas mixtures is found to represent the concentration dependence of the conductivity satisfactorily. The simpler formula for the thermal conductivity of gas mixtures given by Mason and Saxena has also been tested.