Nucleation in superheated argon,krypton and xenon liquids

The superheating of condensed noble gases (argon, krypton, xenon) was investigated by the techniques of continuous heating of liquid specimen in a glass capillary. Experiments covered the pressure range 1–35 bar at the nucleation rates ≈10⁵ cm^-3 s^-1. The superheating data obtained here were compared with the results of calculations based on the Volmer-Becker-Döring-Zeldovich-Frenkel homogeneous nucleation theory. A good agreement between theory and experiment as well as the thermodynamic similarity of the studied substances with respect to the fluctuation nucleation was found.     

Positron annihilation in solid krypton and xenon

A computation of the life time of positrons as well as the angular distribution of the resulting gamma pair for polycrystalline krypton and xenon has been made. The calculations are based on the technique employed by Salvadori and Carbotte for the case of solid argon. The field seen by the positrons is constructed from the charge densities derived from Herman-Skillman wave functions. The positron wave functions are obtained using the Wigner-Seitz approximation. For electrons Herman-Skillman wave functions have been used. The computed distributions, when the effects of correlation are ignored, are wider than the experimental ones. The calculated values for the mean lives of positrons for krypton and xenon are 2.2×10⁻⁹ sec and 2.7×10⁻⁹ sec, respectively, and that for xenon is, as usual, longer than the measured value of 0.43×10⁻⁹ sec. Effects of electronpositron correlations on the angular distribution and the life time have been calculated for the case of krypton. When these corrections are taken into account, the life time of positrons in krypton is reduced by a factor of about eight and the angular distribution shows a slight narrowing. Paper A24 presented at 3rd Internat'l Conf. Positron Annihilation, Otaniemi, Finland (August 1973).     

Equilibrium properties of crystalline argon,krypton and xenon

By assuming an interaction energy for krypton and xenon of the same shape as that established for argon in an earlier paper and without introducing any adjustable parameters, values of the equilibrium properties of the crystals have been calculated which agree with the measured values to within the experimental accuracy or to within one per cent.     

Continuous emission of argon,krypton and xenon plasmas

Emission coefficients of shock-tube plasmas have been measured as functions of the plasma parameters in the visible spectrum. The plasma state was determined by dual-wavelength interferometry and high accuracy of the ξ-factors was achieved. The results are compared with theoretical and other experimental data. In particular, the dependence of ξ on the plasma state is discussed.     

Small-scale electric discharge krypton and xenon chloride laser

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 2, pp. 337–339, August, 1990.     

Environmental perturbations on foreign atoms and molecules in solid argon,krypton and xenon

Perturbations which are responsible for the shifts of electronic and vibrational spectra of species trapped in a solid are considered in terms of the intermolecular potential which describes interactions between these species and neighbouring atoms. It is shown that in certain instances London's theory can give an adequate approximation to the dispersion energy between an electronically excited species and a rare gas atom. The experimental shifts in the electronic absorption spectra of Hg, NH and C₂ at lattice sites in rare gas crystals at 4·2°k are explained quantitatively on the basis of a Lennard-Jones (6-12) or (6-8-12) potential between the trapped species and the rare gas atoms. The theory does not adequately explain the shifts in those cases where strong angular dependent forces differing appreciably in the two electronic states are present, data on trapped NH₂ free radicals being presented as a case in point. The interaction of sodium atoms with argon at 4·2°k is very complex, the data being consistent with multiple trapping sites for the atoms, a large repulsive interaction between the excited state of sodium and the rare gas, and apparent removal of the three-fold orbital degeneracy in the excited state by the environmental perturbation. The three-fold orbital degeneracy in the ³P₁ state of mercury was found also to be removed. The blue shift of 1281 cm^-1 for the ³P₁ ← ¹S₀ transition of mercury in solid argon at 4·2°k corresponds almost exactly with the position of one of the two prominent features in the spectrum of mercury in argon gas at comparable densities and illustrates the similarity of structure in the two physical states. The interesting perturbations on the vibrational states of NH and C₂ suggest a close similarity to the effect which causes environmental variations of coupling constants for hyperfine interactions in trapped hydrogen atoms.     

High-pressure melting curves of argon, krypton, and xenon: deviation from corresponding states theory.

The melting curves of argon, krypton, and xenon were measured in a laser heated diamond-anvil cell to pressures of nearly 80 GPa reaching melting temperatures around 3300 K. For the three gases, we observed a considerable decrease in the melting slopes (dT/dP) from the predictions based on corresponding states scaling starting near 40, 30, and 20 GPa, respectively. The melting anomaly can be understood in terms of a model in which hcp stacking faults act as solutes in a binary system.     

The intermolecular potential energy functions of krypton and xenon

The intermolecular potential energy functions for krypton and xenon have been determined using new semi-inversion techniques. These techniques, which have previously been applied to the data for argon, enable information about intermolecular forces to be obtained directly from second virial coefficient and gas viscosities measurements.     

Photoionization of argon, krypton and xenon clusters in the inner valence shell region

Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer, the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that loses its innershell electron to its neutral partner. Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998     

h.c.p.-f.c.c. phase transition in solid parahydrogen

The difference of free energies for the h.c.p. and f.c.c. parahydrogen is calculated as a function of molar volume. It is shown that the observed transition in solid parahydrogen¹ can be explained by differences in the structure of the cubic and quartic anharmonic terms.     

Derivation of three-body collision-induced light-scattering spectrum moments for argon,krypton, xenon

The expressions for the zeroth and second moments of the three-body component of the collision-induced light-scattering spectrum are derived within the pair-potential and pair-polarizability approximations.

Computer calculation of the three-dimensional integrals which appear in the moment expressions is performed for Lennard-Jones and Barker potentials of argon, krypton and xenon within the dipole-induced-dipole approximation for the pair-polarizability.

The comparison of the results which are obtained with the two different potentials shows the very important role which is played by the choice of the potential in the determination of the values of the moments. An example of the applicability of the moment analysis of the three-body spectrum is also given for argon and the results compared with those of two-body.     

Elementary vibrations in rare-gas crystals: Frequencies of phonons in compressed argon, krypton, and xenon crystals

The lattice dynamics of rare-gas crystals is investigated in the framework of the ab initio approach with the inclusion of the nonadiabatic effects over a wide range of pressures. The frequencies of phonons in argon, krypton, and xenon crystals are calculated at pressures p ≠ 0. Analysis of the contributions from different interactions to the lattice dynamics of the crystals demonstrates that the difference between the phonon frequencies calculated within several models is most pronounced at the boundary of the Brillouin zone. Under strong compressions, the phonon spectrum along the Δ direction is distorted and the longitudinal mode is softened as a result of the electron-phonon interaction, with the relative contribution decreasing in the series Ar, Kr, and Xe. The calculated phonon frequencies are in good agreement with the experimental data available in the literature for argon crystals at a pressure p = 3.1 GPa.     

Dielectric and adsorption isotherms of adsorbed krypton and xenon on boron nitride

We present simultaneous measurements of adsorption isotherms and dielectric isotherms for krypton and xenon on boron nitride. Dielectric measurements give a good characterization of monolayer formation and completion, and provide new information on the dielectric properties evolution from a two-dimensional system towards the bulk.     

Absolute cross sections for collision-induced depolarized scattering of light in krypton and xenon

Depolarized Raman spectra of binary collisional pairs of atoms in krypton and xenon are obtained at gas densities of 1–10 amagat. Absolute intensities relative to a known rotational transition of nitrogen are determined. For light of 4880 Å wavelength incident in the x-direction, polarized in the z-direction and scattered in the y-direction of a cartesian frame x, y, z, at a frequency shift of -12 cm^-1, the differential scattering cross section per unit wavenumber band times volume, is found to be 1·10 × 10^-52 cm⁶ ± 10 per cent for krypton, and 4·76 × 10^-52 cm⁶ ± 10 per cent for xenon, if the sum of both polarizations is considered. Wave-mechanical and classical computations reproduce both the shape and the intensity of the experimental spectra if the so-called point-dipole model of the anisotropy of the polarizability of collisional pairs of atoms is used. Other models of the anisotropy are seen to be overcorrected by these criteria.