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Noble gases are useful tracers for geochemistry, used to elucidate the origin and evolution of the solar system and planets. Noble gas analyses have been limited to bulk and spot analyses of solids and have yet to be developed for two- and three-dimensional imaging analysis. Recent developments in He isotope imaging using secondary neutral mass spectrometry are reviewed. The images have been fully quantified, and the spatial resolution has reached the nanoscale. The detection limit has been reduced to the level of ~ 10–3 cm3 STP g−1 (~ 1017 cm−3, ~ 1 ppma) for helium at lateral micrometer resolution. With this development, the concentration distribution of He in solids has been visualized as a map for the first time. [ABSTRACT FROM AUTHOR]

The Lennard-Jones (LJ) potential is perhaps one of the most widely used models for the interaction of uncharged particles, such as noble gas solids. The phase diagram of the classical LJ solid is known to exhibit transitions between hcp and fcc phases. However, the phase behavior of the quantum LJ solid remains unknown. Thermodynamic integration based on path integral molecular dynamics (PIMD) and lattice dynamics calculations are used to study the phase stability of the hcp and fcc LJ solids. The hcp phase is shown to be stabilized by quantum effects in PIMD, while fcc is shown to be favored by lattice dynamics, which suggests a possible re-entrant low pressure fcc phase for highly quantum systems. Implications for the phase stability of noble gas solids are discussed. For parameters equating to helium, the expansion due to zero-point vibrations is associated with quantum melting: neither crystal structure is stable at zero pressure. [ABSTRACT FROM AUTHOR]

The remarkable success of x-ray free-electron lasers and their ability to image biological macromolecules while outrunning secondary radiation damage due to photoelectrons, by using femtosecond pulses, raise the question of whether this can be done using pulsed high-energy electron beams. In this paper, we use excited state molecular dynamics simulations, with tabulated potentials, for rare gas solids to investigate the effect of radiation damage due to inelastic scattering (by plasmons, excitons, and heat) on the pair distribution function. We use electron energy loss spectra to characterize the electronic excitations responsible for radiation damage. [ABSTRACT FROM AUTHOR]

Closed-shell metal atoms in rare gas solids tend to occupy highly symmetric polyhedral crystal sites, as follows from the generic triplet Jahn-Teller splitting of the S → P excitation bands and complies with the isotropic nature of the dispersion forces. Atypical 2 + 1 Jahn-Teller splitting inherent to axially symmetric sites observed recently for Ba atoms has been therefore interpreted as the defect accommodation. By modeling the structure, stability, and spectra of the Ba atom in the face-centered cubic rare gas crystals, we identify thermodynamically stable crystal site of axial C 3 v symmetry that explains experimental observations. We also demonstrate the dramatic effect of the interaction anisotropy on the trapping site structure and stability for an excited P-state atom. Our results provide strong evidence for stable axially symmetric accommodation of isotropic impurity in a close-packed lattice. [ABSTRACT FROM AUTHOR]

This article provides a summary of recent highlights in the field of supramolecular chemistry. It discusses the importance of ion pairing, even in water, and how it can affect the measurement of association constants. The article also highlights a sensor library that can accurately identify nucleotides, which is challenging due to their similar chemical structures. Additionally, the article explores the use of hydrogen bonding halides to separate noble gases and the synthesis of porous organometallic frameworks. It also mentions a study on the structure of supramolecular cages using DOSY NMR and the assembly of low symmetry metal-organic cages. Lastly, the article discusses the association of oligourea foldamers with surfactants. [Extracted from the article]

Monte Carlo simulations of low-energy (< 50 keV) electron transport in matter are essential for a broad range of application fields. Several Monte Carlo codes have developed specialized treatments for this case, but a comprehensive validation of low-energy electron transport for general-purpose simulations remains lacking in the literature. One approach to accomplish this validation is calculation of stopping power using low-energy electron transport physics, as stopping power is a fundamental radiation transport quantity which must be simulated accurately for nearly any application. In this work, we use the Monte Carlo N-Particle (MCNP) radiation transport code with the single-event method for electron transport to calculate stopping powers of low-energy electrons (50 eV to 30 keV) in 41 elemental solids, 14 compound solids, and five rare gas solids, comparing simulation results to published semi-empirical stopping power calculations from optical measurements. In general, the simulations give good agreement (typically within ± 10%) with semi-empirical stopping power values at higher energies: 300 eV and above for most elemental solids, 1 keV and above for compound solids, and 400 eV and above for rare gas solids. Agreement between MCNP and semi-empirical values is worse below these energies. The most significant source of error is the EPRDATA14 cross section data, which does not account for changes in electronic structure due to solid-state bonding, particularly in compound materials. The simplistic model of atomic excitation used to generate the EPRDATA14 cross sections is another key source of error. Additionally, the breakdown of the continuous slowing-down approximation introduces significant uncertainty at low energies, although this is a limitation of the calculation method and not of the simulation procedure. Accounting for these and other uncertainty sources, the single event method in MCNP is robust and able to give good accuracy for a variety of low-energy electron transport problems through diverse kinds of materials. • General validation of low-energy electron transport by the single-event method. • Strong agreement with semi-empirical stopping powers for electrons above 300 eV. • Divergence for electrons below 300 eV due to uncertainty in cross section data. • Performance for compound materials is weaker due bonding effects on cross section. [ABSTRACT FROM AUTHOR]

Classical simulations of model O( 3 P) atom isolated in Ar, Kr and Xe crystals with the variable magnitude and sign of the angular momentum anisotropy are performed. The guest–host interaction anisotropy remarkably affects the structure of the atomic trapping sites and the barriers to the temperature-induced atomic mobility. For interstitial trapping, inversion of anisotropy induces a kind of critical phenomenon, which transforms the migration path saddle point to a minimum and another saddle. As a result, a new peculiar axially symmetric interstitial site is formed with the migration barrier reduced. Preliminary ab initio-based study of the C( 3 P) atom, whose interactions with Ar, Kr and Xe have the anisotropy opposite to oxygen, fully confirms the model analysis. Our results emphasise profound effect of the angular momentum anisotropy on the structure and dynamics of the open-shell atoms at matrix isolation. [ABSTRACT FROM AUTHOR]

The effect of magnetic field, the ratio of the density of solid particles to the initial density of the gas, non-idealness of the gas, mass concentration of micro size solid particles, adiabatic exponent, and the heat transfer parameters effect on one-dimensional shock wave propagation in a dusty gas with conductive and radiative heat fluxes in the presence of azimuthal or axial magnetic field in rotating medium have been investigated for cylindrical geometry. By using the similarity method a system of ordinary differential equations are derived from the system of governing equations of motion. The dusty gas is taken to be perfectly conducting mixture of non-ideal gas and small inert solid particles of micro size, in which solid particles are continuously distributed. It is understood that variable energy input is constantly supplied by the moving piston and the equilibrium flow conditions are maintained in the whole flow-field region. The results of numerical integration for the system of ordinary differential equations show that the magnetic field, mass concentration of solid particles, the ratio of the solid particles density to the gas initial density, non-idealness of the gas, adiabatic exponent and the heat transfer parameters have strong influence on the shock wave and on the flow variables. It is found that the presence of magnetic field, an increase in conductive and radiative heat transfer parameters and non-idealness of the gas have decaying effect on the shock wave; whereas the ratio of the solid particles density to the gas initial density or the adiabatic exponent have effect to increase the shock strength. • MHD shock in rotating dusty gas with conductive and radiative heat fluxes is modelled. • Shock strength decreases with non-idealness of the gas and magnetic field. • Density and pressure vanish at the piston i.e. a vacuum is formed at axis of symmetry. • Shock strength increases with adiabatic exponent, and the density ratio of solid particles and that of gas. • Radiative and conductive heat transfer parameters both increase the shock strength. [ABSTRACT FROM AUTHOR]

To obtain insights into the mechanism of the melting-point depression of rare gas solids confined in crystalline carbon pores, we examined the freezing and melting behavior of Xe and Ar confined to the crystalline pores of ordered mesoporous carbons as well as compressed exfoliated graphite compared to the amorphous pores of ordered mesoporous silicas, by means of X-ray diffraction. For the Xe and Ar confined to the crystalline carbon pores, there was no appreciable thermal hysteresis between freezing and melting. Furthermore, the position of the main diffraction peak did not change appreciably on freezing and melting. This strongly suggests that the liquids confined in the carbon pores form a multilayered structure parallel to the smooth walls. For the Xe and Ar confined to the amorphous silica pores, on the other hand, the position of the main diffraction peak shifted into higher scattering angle on freezing suggested that the density of the confined solid is distinctly larger than for the confined liquid. Using compressed exfoliated graphite with carbon walls of higher crystallinity, we observed that three-dimensional (3D) microcrystals of Xe confined in the slit-shaped pores melted to leave the unmelted bilayers on the pore walls below the bulk triple point. The lattice spacing of the 3D microcrystals confined is larger by ~0.7% than that of the bilayer next to the pore walls in the vicinity of the melting point. [ABSTRACT FROM AUTHOR]

The fluoronitrenoid metal complexes FNCoF2 and FNRhF2 as well as the first ternary RhVI and IrVI complexes NIrF3 and NRhF3 are described. They were obtained by the reaction of excited Group‐9 metal atoms with NF3 and their IR spectra, isolated in solid rare gases (neon and argon), were recorded. Aided by the observed 14/15N isotope shifts and quantum‐chemical predictions, all four stretching fundamentals of the novel complexes were safely assigned. The F−N stretching frequencies of the fluoronitrenoid complexes FNCoF2 (1056.8 cm−1) and FNRhF2 (872.6 cm−1) are very different and their N−M bonds vary greatly. In FNCoF2, the FN ligand is singly bonded to Co and bears considerable iminyl/nitrene radical character, while the N−Rh bond in FNRhF2 is a strong double bond with comparatively strong σ‐ and π‐bonds. The anticipated rearrangement of FNCoF2 to the nitrido CoVI complex is predicted to be endothermic and was not observed. [ABSTRACT FROM AUTHOR]

The fluoronitrenoid metal complexes FNCoF2 and FNRhF2 as well as the first ternary RhVI and IrVI complexes NIrF3 and NRhF3 are described. They were obtained by the reaction of excited Group‐9 metal atoms with NF3 and their IR spectra, isolated in solid rare gases (neon and argon), were recorded. Aided by the observed 14/15N isotope shifts and quantum‐chemical predictions, all four stretching fundamentals of the novel complexes were safely assigned. The F−N stretching frequencies of the fluoronitrenoid complexes FNCoF2 (1056.8 cm−1) and FNRhF2 (872.6 cm−1) are very different and their N−M bonds vary greatly. In FNCoF2, the FN ligand is singly bonded to Co and bears considerable iminyl/nitrene radical character, while the N−Rh bond in FNRhF2 is a strong double bond with comparatively strong σ‐ and π‐bonds. The anticipated rearrangement of FNCoF2 to the nitrido CoVI complex is predicted to be endothermic and was not observed. [ABSTRACT FROM AUTHOR]

In this study, we investigate the electronic and optical properties of rare gas solids Kr and Ar in detail using the first principle calculation. A full potential linearized augmented plane wave method has been employed in conjunction with the Tran Blaha modified Becke-Johnson potential plus local density approximation and the generalized gradient approximation exchange correlation potentials. We have found that the studied rare gas solids have insulator nature with large gap energy of order of 10.523 eV and 13.673 eV for Kr and Ar, respectively. The obtained electronic results are in good agreement with the available experimental and theoretical data. The optical properties, including the reflectivity R(w), the absorption coefficient α(w), the energy loss function L(w), the refractive index n(w) and the extinction coefficient k(w) are deduced from real and imaginary parts of the calculated dielectric function within the modified Becke–Johnson plus local density approximation and generalized gradient approximation exchange correlation potentials. We have found a direct band gap for the two rare gas solids, good refractive index, large absorption band between 10 and 20 eV. This is the first quantitative theoretical prediction of the optical properties for the two rare gas solids that requires experimental confirmation. The obtained results can be exploited for the application in optoelectronics. [ABSTRACT FROM AUTHOR]

Pulsed laser irradiation of solid potassium cyanide (KCN) produces, besides free nitrogen and carbon atoms, the molecular species KN and KC which are potential candidates for interstellar species of potassium. Additionally, N3, N3−, KN3, C3, C3−, and KC3 are produced and isolated in solid noble gases as well as in solid N2. Molecular potassium nitrene (KN) reacts with dinitrogen in neon and argon matrices after photochemical excitation (λ=470 nm) forming molecular end‐on (C∞v) and side‐on (C2v) potassium azide isomers. The side‐on isomer (C2v) is thermodynamically favored at the CCSD(T)/ma‐def2‐TZVP level of theory. It can be obtained from the end‐on isomer by UV‐irradiation (λ=273 nm). [ABSTRACT FROM AUTHOR]

The classical model of an ideal crystal, parametrized according to non-empirical calculations, is used to determine the structure and geometry of the atomic lithium trapping sites in solid inert gases RG = Ar, Kr, and Xe, and to define their thermodynamic stability. The diversity of the observed stable sites reduces to four highly symmetric structures corresponding to the interstitial introduction of an Li atom, its substitution of an inert gas atom, or its incorporation into tetrahedral and octahedral vacancies formed by the removal of four and six inert gas atoms from the crystal lattice. The non-empirically calculated dependences of the isotropic hyperfine coupling constant tensor on the distance in the diatomic Li@RG complex are used to estimate the shifts of the electron paramagnetic resonance signals in the predicted thermodynamically stable sites. A comparison with published data does not contradict the assignment of the observed multiple signals to certain types of stable sites, taking into account the spectral features of samples that were prepared by thermal deposition and laser ablation in three different inert gases. [ABSTRACT FROM AUTHOR]

We have developed a new experimental apparatus for performing coincidence measurements of the ions desorbed and projectiles scattered from the surfaces of noble gas solids by slow multiply charged ion impacts at grazing incidence angles. This simultaneously measures the desorbed ions' flight times and the scattered projectiles' charge states. We also conduct experiments on 6 keV Ar6+ impacts onto a solid Ne surface using the device. [ABSTRACT FROM AUTHOR]

Site-selective excitation has been used to simplify complex emission recorded in the visible spectral region for atomic europium isolated in the solid rare gases. In addition to y8P resonance fluorescence, excitation of the y8P state produces emission from the z6P state and the metastable a10D state. Very weak emission at 690 nm is tentatively assigned to the J = 9/2 level of the z10P state. Eu atoms isolated in the red and blue sites exhibit very different temperature dependence both spectrally and temporally. For the y8P state emission the red site atoms exhibit small Stokes shifts and yield radiative lifetimes while the emission from the blue site loses intensity and the temporal profiles shorten dramatically between 10 and 16 K indicating very efficient non-radiative relaxation in this site. An analysis of the Stokes shifts exhibited for the y8P state in each site supports the attributions made in a previous publication [O. Byrne and J.G. McCaffrey, J. Chem. Phys. 134, 124501 (2011)] that the smaller blue tetravacancy site has a greater repulsive interaction with the guest. With the exception of the y8P state resonance fluorescence, the recorded decay profiles of all the other emissions exhibit multiple components. This behaviour has been attributed to the existence of multiple crystal field levels arising from the splitting of the distinct spin-orbit levels from which emission occurs. [ABSTRACT FROM AUTHOR]

Absorption spectroscopy recorded for annealed samples of matrix-isolated atomic europium reveals a pair of thermally stable sites in Ar and Kr while a single site exists in Xe. Plots of the matrix shifts of the visible s → p bands versus host polarizability, allowed the association of the single site in Xe and the blue sites in Ar and Kr. On the basis of the similar ground state bond lengths expected for the Eu-rare gas (RG) diatomics and the known Na-RG molecules, the blue sites are attributed to Eu occupancy in the smaller tetra-vacancy while the red sites are proposed to arise from hexa-vacancy sites. Both sites are of cubic symmetry, consistent with the pronounced Jahn-Teller structure present on the y8P ← a8S7/2 transition for these bands in the three hosts studied. Site-selective excitation spectroscopy has been used to reanalyze complex absorption spectra previously published by Jakob et al. [Phys. Lett. A 57, 67 (1976)] for the near-UV f → d transitions. On the basis that a pair of thermally stable sites exist in solid argon, the occurrence of crystal field splitting has been identified to occur for the J ≥ 5/2 level of the 8P state when isolated in these two sites with cubic symmetry. From a detailed lineshape analysis, the magnitude of the crystal field splittings on the J = 5/2 level in Ar is found to be 105 and 123 cm-1 for the red and blue sites, respectively. [ABSTRACT FROM AUTHOR]

The stepwise three-photon two-color laser excitation scheme is used for selective population of the first-tier ion-pair D0+u state of molecular iodine. Collection and analysis of the luminescence after the excitation of the vD = 6, 8, 13 and 18 vibronic levels of the D state in the pure iodine vapor and the gas-phase mixtures with He, Ar and Xe provide the total and, whenever possible, partial rate constants for the collision-induced non-adiabatic transitions to the other ion-pair states of the first tier. Comparison with the analogous data obtained previously for the non-adiabatic transitions from the E0+g state reveals the similarity between two cases. For He, the D ↔ E transitions are preferable, whereas for Ar and Xe transitions to the D′ and β states dominate at vD = 6, 8 and 13, in accord with the statistical considerations. Efficient population of the δ state at vD = 18 in Ar and Xe is the most prominent non-statistical feature observed. The vibrational product state distributions for the D → E transitions are also obtained. In contrast to the previously studied E → D transition, they show significant positive vibronic energy transfer. The measurements for He and Ar are accompanied by the quantum scattering calculations that reproduce well the main qualitative features of the experimental results. [ABSTRACT FROM AUTHOR]

The 193 nm laser irradiation of cyanoacetylene (HCCCN) that was isolated in rare gas solids led to a long-lived luminescence (origin at 3.58 eV), which was assigned to the ã 3Σ+-X 1Σ+ system of cyanoacetylide (CCCN-). The identification, which involved 15N and 2H isotopic substitution studies, is based on vibronic spacings in the phosphorescence spectrum (compared to previous infrared absorption measurements and to theoretical results regarding CCCN- vibrational frequencies), as well as on a BD(T)/cc-pVTZ prediction for the singlet-triplet energy gap in this anion (3.61 eV). The same emission was also generated from Kr/HC3N mixtures subjected to a glow electric discharge immediately before the solidification (cold-window-radial-discharge technique). [ABSTRACT FROM AUTHOR]

Effect of particle size on exchange bias observed in Fe/Fe oxide core/shell structured nanoparticles was investigated. Inert gas condensation was utilized for the synthesis of samples. Two sets of different particle size samples were prepared and the structural and magnetic properties were probed. It was found that the small particles show superparamagnetic behavior and exhibit high exchange bias field, 1574±25 Oe at 5 K, when field cooled in the presence of 2 T magnetic field. Structural analyses of the particles in correlation with the magnetic measurements show that the smaller particle size (6 nm Fe core, 1.5 nm Fe oxide shell) favors amorphous oxide shell structure, and this in turn causes high magnetocrystalline anisotropy and enhanced exchange bias. Furthermore, we have also observed a vertical shift of the hysteresis loop related to the pinned spins at the ferromagnetic/antiferromagnetic (AFM) interface of the small particles. Decreased core size, high AFM anisotropy, and pinned spins observed from the small size particles support the domain wall model of the exchange bias. [ABSTRACT FROM AUTHOR]

The transport properties of Co/Al2O3/Co magnetic tunnel junctions with ion-irradiated tunneling barrier are reported. The irradiation by He+ and Ar+ with energies ranging from 15 to 105 eV takes place in situ after oxidation of the 1.4-nm-thick Al layer. For both ion species the area resistance of the junctions increases strongly with ion energy, simultaneously the tunneling magnetoresistance is reduced. But the energy dependence of both properties is different for He+ and Ar+ irradiations. Additionally the bias voltage dependence of the tunneling magnetoresistance is deteriorated with increasing ion energy especially for Ar+ irradiation. These experimental results are discussed with respect to the energy-dependent penetration depth of He+ and Ar+ and their energy loss in the barrier. [ABSTRACT FROM AUTHOR]

The initial stages of vapor condensation of Ge in the presence of a cold Ar atmosphere were studied by molecular-dynamics simulations. The state variables of interest included the densities of condensing vapor and gas, the density of clusters, and the average cluster size, while the temperatures of the vapor and the clusters were separately monitored with time. Three condensation processes were explicitly identified: nucleation, monomeric growth, and cluster aggregation. Our principal finding is that both the average cluster size and the number of clusters scale with the linear dimension of the computation cell, L, and Ln, with the scaling parameter n≈4, corresponding to a reaction order of ν≈2.33. This small value of n is explained by an unexpected nucleation path involving the formation of Ge dimers via two-body collisions. [ABSTRACT FROM AUTHOR]

We have developed a simple model to simulate the clusters formation in laser-ablated plume in an ambient atmosphere of inert gas. The model uses the reaction-rate theory as applied to quantum oscillators in conjunction with transition state theory to synthesize and optimize the nanoparticles in the ablated plume. The evolution of cluster size is obtained by incorporating diffusion of ambient gas into an adiabatically expanding plume. Various rate constants of clustering reactions are calculated using collision rate and transition state theory. We have used the model to simulate the spatial and temporal extents of silicon nanoparticle formation in laser-ablated silicon plume generated using 248- and 532-nm irradiation in ambient atmosphere of argon. The model predicts the onset time of 3 ms with 248 nm and 1.0 Torr of argon and 2.0, 1.2, and 0.6 ms with 532-nm irradiation and argon background at 2, 5, and 10 Torr, respectively, for 1-nm clusters of silicon. The concentration of clusters decreases with an increase in distance from the target surface. The onset time dependence on ambient pressure follows a simple relation of the form {τonset∝(1/Pambient)0.91}. The reasonable agreement of simulated results with experimental observations implies that the model is adequate to simulate Si cluster formation in the ablation plume. [ABSTRACT FROM AUTHOR]

We investigate the hydrodynamic properties of liquified-inert-gas jets in a vacuum with a special emphasis on their stability. Such jets have applications as targets for laser–plasma generation of soft-x-ray and extreme-ultraviolet (EUV) radiation. An important example is the liquid-xenon-jet laser-plasma source, one of the source candidates for EUV lithography. A simple hydrodynamic model in not sufficient to explain experimental observations of jet stability. Evaporation-induced cooling explains observed in-flight freezing of the jet and may be a key factor influencing jet stability. It is shown how the jet stability, and, thus, the stability of the laser–plasma x-ray and EUV emission, are improved by applying localized heating to the tip of the jet-generating nozzle. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The relaxation of the higher-energy cis conformer of formic acid to the lower-energy trans form by a tunneling mechanism has been investigated in low-temperature rare gas matrices. In the temperature range 8-60 K, the tunneling takes place dominantly from the vibrational ground state of the cis form and the temperature dependence of the tunneling rate constant is influenced by the interactions with the environment. The temperature-dependent tunneling rates for HCOOH and DCOOH in solid Ar, Kr, and Xe are measured including data for molecules in different local environments within each host. It was found that the medium and the local environment has a significant influence on the tunneling rate. [ABSTRACT FROM AUTHOR]

The vibrational spectroscopy and the matrix-site geometries of several novel rare-gas compounds in the matrix environment were computed theoretically, and compared with experiment. Ab initio calculations are used in the fitting of analytical potential surfaces for the HRgY molecules and for the interactions between HRgY and the matrix atoms Rg. With these potentials, matrix-site geometries for the molecule in the solid are computed. Finally, the vibrational spectroscopy of HRgY in the Rg matrix is computed using the vibrational self-consistent field (VSCF) method. The VSCF includes anharmonic effects, that are essential in this case. The version of VSCF used here includes coupling between HRgY and the vibrations of the solid atoms. The vibrations of 72 matrix atoms are treated. The main results are: (1) The matrix shifts are considerably greater than typically found for neutral, strongly bond molecules, but are much smaller than discrepancies between theory and experiment. This can be attributed to the insufficient accuracy of the potentials used for the HRgY molecules. This calls for better future description of the electronic structure of HRgY. (2) The matrix shifts and splitting effects are interpreted by the calculations in terms of the site geometries involved. These effects are very different for HArF, HKrF than for HXeCl, HXeI. (3) The computed matrix-site splittings are in semiquantitative accord with experiment. This supports the interaction potentials used between HRgY and the matrix. The results provide insights on the effects of the matrix on the rare-gas molecules. [ABSTRACT FROM AUTHOR]

This study measured the absolute ion desorption yield from the surface of solid Ne and Ar by low-energy Neq+ (q = 1–4), Arq+ (q = 1–6), and Krq+ (q = 2–6) ion impacts. Results revealed the dependence of ion desorption yield on the potential and the kinetic energies of the incident ions, as well as its linear proportionality with the former. Present results could not be explained by existing models for ion desorption from insulator surfaces. We proposed a new mechanism of ion desorption that considers the contribution of both energy types to ion desorption. [ABSTRACT FROM AUTHOR]

A molecular dynamics deposition model has been used to simulate the growth of rare gas matrices doped with atoms of the group 12 elements zinc, cadmium and mercury. This study investigates the sites occupied by Zn, Cd and Hg metal atoms when isolated in the solid rare gases. To probe the results, the resonance 1 P 1 ← 1 S 0 transitions of the matrix-isolated metal atoms were calculated and compared with the recorded spectra of the M/RG solids. The theoretical spectroscopy obtained in this work was generated using the molecular dynamics with quantum transitions method. In Ne matrices the metal atoms preferably occupy tetra- and hexa-vacancy sites while in the case of Xe matrices, only the single vacancy site is formed. For Ar and Kr matrices Zn but especially Cd can be trapped in tetra- and hexa-vacancy sites in addition to single-vacancy sites, while Hg atoms show exclusive occupancy in single vacancy sites. [ABSTRACT FROM AUTHOR]

The isochoric thermal conductivity of Kr0.63Xe0.37 solid solution has been investigated for three samples with different molar volumes in the temperature range from 80 K to the onset of melting, as well as the thermal conductivity of the ternary (Kr0.63Ar0.185Xe0.185) and quaternary (Kr0.63Ar0.12Xe0.12(CH4)0.13) solid solutions. It is found that for multi-component alloys, the thermal conductivity reaches a minimum, whereby adding more impurity atoms in the solid solution does not affect the thermal conductivity in agreement with the recent nonequilibrium molecular dynamics calculations for argon. The phonon contribution to the total thermal conductivity depends significantly on molar volume of sample and impurity concentration, in contrast to the contribution of diffusive modes, which is practically independent of these factors. [ABSTRACT FROM AUTHOR]

Reports that the ultraviolet (UV) irradiation of rare-gas solid-doped xenon matrix dissociates the precursor and leads to the formation and trapping of neutral atoms. Annealing of the matrix to mobilize the hydrogen atoms; Kinetic measurements; Validity of the formation mechanism from neutral atoms for other similar rare-gas compounds.

Reports on the laser induced fluorescence spectra of the thiohydroxyl radical inert gas complexes. Spectra of numerous isotopomers; Observed transition frequencies; Dissociation energies.

Examines the high resolution laser induced fluorescence spectra of the hydroxyl radical inert gas complexes. Inclusion of rotation, fine and hyperfine structure, spin-rotation interactions and parity splitting in the analysis of bands; Determining a number of molecular parameters.

Studies the simulation of atomic zinc luminescence in rare gas solids. Comparison with theoretical predictions obtained from the sum of diatomic pair potentials; Ground X electronic state; Calculations of the stabilization energy arising from the motion; Waist mode stabilization energy; Excited triplet states.

Dissociation efficiencies for excitation of the repulsive A 1Π state of HCl were recorded in Xe, Kr, and Ar matrices for photon energies between 5 and 10 eV from the content of dissociation products and quantum efficiencies were derived with the absorption spectra. Influence of temperature and preparation conditions was investigated. The quantum efficiency rises monotonically in Xe from an excess energy of 1.4 eV above the gas phase dissociation energy on, saturates around 2.4 eV and remains then essentially constant up to 4 eV. In Ar and Kr, it saturates around 2 eV and in Ar an absolute efficiency of about 0.18 is determined at 3.7 eV. Results of molecular dynamics calculations and a statistical model agree qualitatively but the observed saturation at low excess energies is not well described and the absence of a temperature effect in Ar needs further consideration. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The surface rigidity and corrugation of the liquid metals indium, gallium, and bismuth are investigated by scattering neon, argon, and xenon from each liquid. The inert gas fractional energy transfers and trapping–desorption fractions are much lower for these atomic liquids than for molecular fluids, reflecting the high mass densities and high surface tensions of the liquid metals. The peak energy transfer at a 55° specular angle can be predicted by using hard sphere collision mechanics and by estimating the mass ratio μ=mgas/msurf by (0.28±0.02 Å-1) (ρgas/ρliq), where ρgas is the mass per cross-sectional area of the gas atom and ρliq is the bulk metal density. The specular scattering intensity decreases as the liquid’s temperature increases at a fractional rate approximately equal to -1/(2Tliq). The intensity appears to scale nearly inversely with the amplitude of the surface atom fluctuations. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Pure rotational spectra of several isotopomeric species of the rare gas dimers Ne–Kr and Ar–Kr have been measured using a pulsed jet cavity microwave Fourier transform spectrometer. Equilibrium internuclear distances have been evaluated by taking advantage of the isotopic data, for both these dimers and three Xe-containing dimers, whose spectra were reported earlier [Jäger et al., J. Chem. Phys. 99, 919 (1993)]. The dipole moments have been estimated using the ‘‘π/2-pulse’’ excitation condition. 83Kr nuclear quadrupole hyperfine structure has been observed in some rotational transitions of 20Ne–83Kr and of Ar–83Kr, and the corresponding quadrupole coupling constants have been derived. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A general statistical theory is proposed here to calculate the Gibbs energy of multicomponent mixtures. This theory is based on the assumptions of the quasichemical approximation and on the unsymmetrized self-consistent-field method. The effectiveness of the proposed theory is demonstrated through its application to determine vacancy formation parameters in rare gas solids (Ar, Kr, and Xe). In the calculations the pair potentials of Lennard-Jones and Barker et al. are used. The third-order triple-dipole forces of Axilrod–Teller–Muto are taken into consideration. The results are compared with the available theoretical calculations, Monte Carlo computations, and experimental estimations for some parameters of the vacancy formation. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Atomic resonances of the group 12 metal atoms, Hg, Cd, and Zn, undergo frequency shifts from the gas phase atomic line when trapped in rare gas matrices of Ar, Kr, and Xe at 12 K. As expected, the shifts are approximately linear in polarizability of the rare gas, but the slope of this line depends on whether the transition in question is 1P1←1S0 or 3P1←1S0. Thus the matrix-induced frequency shift is dependent on the singlet or triplet nature of the excited state as well as on the matrix material. This dependence on multiplicity is discussed in terms of interactions between the excited-state atomic orbitals and the matrix. The results are compared to matrix studies of other metals and to related gas-phase work on diatomic van der Waals complexes of group 12 metals with rare gases. [ABSTRACT FROM AUTHOR]

We have developed perturbative expressions for the adiabatic potential for alkali–inert gas systems. The predictions of the model for the equilibrium separation Rm and the minimum potential εm are in good agreement with the experimental values. The model provides a unified approach to the interaction potential which indicates a conformal structure for some groups, implying a useful relation between Rm, εm, and van der Waals constant C6. [ABSTRACT FROM AUTHOR]

The electron spin resonance spectra of VC, VSi, NbC, and NbSi trapped in the solid rare gases (Ne, Ar, Kr) show, principally through the large negative values of Δg||=g||-ge, that the orbital angular moments of these molecules in their (proposed) ground 2Δ states are partially quenched. Observed metal hyperfine splittings also vary with the matrix gas. This unprecedented effect in rare-gas matrices is attributed to strong unsymmetrical interaction of these ionic molecules with the matrix such that each is situated in an orthorhombic crystal field. The crystal-field-splitting parameter δ is both molecule and matrix dependent, varying from approximately 1400 to 7800 cm-1. [ABSTRACT FROM AUTHOR]

We have analyzed the interaction of inert-gas atoms with some closed-shell ions such as alkali and alkaline-earth ions. A perturbative approach leading to exchange-Coulomb and asymptotic terms allows us to calculate the equilibrium properties of the cluster molecules formed by these systems. [ABSTRACT FROM AUTHOR]

Direct measurements have been made on the average single-particle kinetic energies, , of a series of solid and liquid specimens of heavy noble gases near melting. To do this, the distributions of energy losses of incident eV neutrons, scattered at angles ranging from 87 to 136 deg, were analyzed on the assumptions that atoms in these specimens have a Gaussian momentum distribution n(p) and that for these experimental conditions the atoms scatter independently of one another. It is known that the solids, Ar, Kr, and Xe show considerable differences in such characteristics as (a) their respective ratios of triple point to Debye temperatures, (b) the extent of multibody force contributions to cohesion, and (c) phonon anharmonicity. Regardless, it is found for all three solids near their respective triple points that is equal to the equipartition value (3/2)kT well within the various estimated experimental uncertainties of 3% to 7%. Moreover, liquid Kr near its triple point yields the same result, as does liquid Xe at temperature up to 1.8 times its triple point temperature. Because all these systems are expected to be classical at these temperatures, these results demonstrate applicability of this neutron recoil method to determine even of heavy atoms in suitable cases where a value may not be known in advance. [ABSTRACT FROM AUTHOR]

Presents a study that described ultrafine metal particles produced by evaporation in an inert gas connect into large clusters by a fractal dimension at length scales less than a correlation length. Development of an effective medium theory for fractal structures; Presence of a structural parameter which can related to the fractal dimension; Results of the comparisons of experimental results on the optical properties of gas-evaporated coatings.

We have synthesized hcp-Co fine particles with the average diameter of less than 50 nm by sputtering Co in a somewhat high inert gas pressure. A nearly perfect hcp phase can be stabilized by increasing sputtering gas pressure and decreasing sputtering power in contrast to conventional preparation conditions. Magnetic measurements have revealed the clear relation of coercivity with the volume ratio of hcp phase. That is, the increase in the hcp phase considerably enhances the coercivity. Appearance of the hcp phase seems to be related to the promotion of allotropic phase transformation in Co initiated by lattice defects within each particle. [ABSTRACT FROM AUTHOR]

The repulsive wall of the Ar–Ar interaction is reexamined with the purpose of rationalizing the apparent inconsistency between high energy beam results and high temperature transport data. A new piece-wise experimental potential is proposed which predicts not only the beam results but a large set of transport data up to 7000 K. Lower temperature/energy data are predicted almost equally as well as other state-of-the-art empirical potentials. [ABSTRACT FROM AUTHOR]

Classical molecular dynamics simulations of sputtering using large samples of up to 15 500 particles are demonstrated for Lennard-Jones solids. Two features are introduced to represent the effect of the surrounding solid substrate. First, the outermost particles on each side of the sample are subjected to an additional harmonic potential restraining them close to the equilibrium position. Second, these outermost particles are maintained at a preset temperature by assigning velocities at each time step randomly from the corresponding Gaussian distribution. This boundary thermostat produces a ‘‘sandbag’’ effect and provides a means for excess kinetic energy to dissipate out of the sample. Preliminary results were obtained for single trajectories at 45° incidence and these illustrate that the sputtering yield from these model rare gas solids is strongly dependent on both the length of the simulation and the size of the sample. Simulations were continued to times in excess of 25 ps after which time for the largest sample there was some recoalescence of particles remaining in the surface region of the substrate. The long time sputtering yield was about 500 atoms which is comparable with experimental data on rare gas solids. It is demonstrated that particles within a cluster are just as likely to arise from nonadjacent sites as from near neighbors in the original lattice. [ABSTRACT FROM AUTHOR]