Kr Atoms Research Articles

Production efficiencies of Kr*(1s5,1s4) atoms leading to vacuum-ultraviolet emissions in ac plasma display panels with Kr–Ne binary mixtures measured by laser-absorption spectroscopy

Ne–Kr gas mixtures with high Kr concentrations were applied to ac plasma display panels. Spatiotemporal behaviors of excited Kr atoms in the 1s5 metastable state and the 1s4 resonance state were measured by microscopic laser-absorption spectroscopy in the binary mixtures with Kr concentrations of 20% and 40%. A systematic comparison was done between the characteristics of Ne–Kr-filled panels and those of conventional Ne–Xe panels with the same structure but with lower Xe concentrations of 5% and 10%. For example, the total number of Kr*(1s5) atoms in a unit cell ranged from 7.4×107 to 2.0×108, at the peak was apparently smaller than the value of Xe*(1s5) atoms. However, when the difference in the decay rate of the excited atoms by three-body collision processes is taken into account, the production efficiency of vacuum-ultraviolet (VUV) emission from Kr2* excimers is as large as that from Xe2* excimers in a usual panel since these processes lead directly to the formation of excimers. From the measured density of Kr*(1s4) atoms, it is estimated that the contribution of the atomic resonance line is smaller than the excimer band at those high Kr concentrations. In any case, by summing up those two contributions to the VUV emission, the overall efficiency in the Ne–Kr(40%) panel is estimated to be comparable to that in the Ne–Xe(10%) one.

Mechanism of adsorption in cylindrical nanopores: The roles of fluctuations and correlations in stabilizing the adsorbed phase

The mechanism of the adsorption in nanometric cylindrical pores has been studied using grand canonical Monte Carlo simulations. The results have been analyzed from the point of view of microscopic correlations. It has been shown that the correlations between the energy components and between the energy and the number of adsorbed particles provide crucial information concerning the microscopic mechanism of the formation of adsorbed layers. Typical susceptibility functions have been calculated. They give the relations between the statistical correlations and the stability of the adsorbed system in different stages of adsorption. The numerical calculations have been carried out for Kr atoms adsorbed in an MCM-41 model porous material with pores of diameter d = 4 nm. The smooth-wall model as well as the model of a wall with micropores have been discussed.

Supercollisions and energy transfer of highly vibrationally excited molecules

Collisional energy-transfer probability distribution functions of highly vibrationally excited molecules and the existence of supercollisions remain as the outstanding questions in the field of intermolecular energy transfer. In this investigation, collisional interactions between ground state Kr atoms and highly vibrationally excited azulene molecules (4.66 eV internal energy) were examined at a collision energy of 410 cm-1 using a crossed molecular beam apparatus and time-sliced ion imaging techniques. A large amount of energy transfer (1000-5000 cm-1) in the backward direction was observed. We report the experimental measurement for the shape of the energy-transfer probability distribution function along with a direct observation of supercollisions.

Rare Gas Effects on Hyperfine Coupling Constants of BO, AlO, and GaO

Using density functional theory methods and large basis sets, we calculated hyperfine coupling constants (HFCCs) for the (11)B, (17)O, (27)Al, and (69)Ga nuclei of the radicals BO, AlO, and GaO (XO), embedded in 2-14 rare gas (Rg) Ne and Ar atoms. Kr atoms were included for AlO. The distance of the Rg atoms from XO was varied from 4 to 12 bohr. Matrix effects cause A(iso)(X) to increase, accompanied by decreases in A(dip)(X) and A(dip)(O), while A(iso)(O) remains close to zero. Changes are largest for AlO, slightly smaller for GaO, and very small for BO, in line with the molecular polarizabilities. Observed changes of A(iso)(X) and A(dip)(X) for BO in Ne matrixes and for AlO in Ne, Ar, and Kr matrixes are reproduced in complexes with 12 Rg atoms at distances of 5-6 bohr or 14 Rg atoms at distances of 6-7 bohr. For GaO, experimental data are available only in Ne matrixes. Theoretical results obtained for HFCCs of (17)O could not be verified due to insufficient experimental information. Estimates of HFCCs in matrixes not yet experimentally studied and for GaO in the gas phase have been made. Due to the interaction with rare gas atoms, p-spin density on the X and O atoms of XO is converted into s-spin density on X, thereby causing an increase (in magnitude) of A(iso)(X), accompanied by decreases in A(dip) of X and O. The higher polarizability of XO along the bond axis is reflected in complexes that have axial Rg atoms showing larger changes in HFCCs than comparable complexes without axial Rg atoms.

Frequency-dependent hyperpolarizabilities of the Ne, Ar, and Kr atoms using the approximate coupled cluster triples model CC3

The frequency-dependent electric field-induced second harmonic generation (ESHG) second hyperpolarizabilities gamma of neon, argon, and krypton are calculated using the approximate coupled cluster triples model CC3. Systematic basis set investigations are carried out to establish basis set limits, and scalar relativistic effects are accounted for by direct perturbation theory. To estimate higher-order correlation effects, full configuration-interaction results are used to benchmark the accuracy of CC3. The best theoretical estimates obtained thereby for the static second hyperpolarizabilities gamma(0) are 107.4, 1159, and 2589 a.u. for neon, argon, and krypton, respectively. These values as well as the results for the dispersion curve of the parallel component gamma( parallel) agree well with the latest experimental values from electric field-induced second harmonic generation. In addition, the dispersion of the perpendicular component gamma( perpendicular) and the hyperpolarizability ratios gamma( parallel)gamma( perpendicular) has been studied for the first time on a consistently correlated ab initio level. The analysis of the results indicates that, in particular for neon and krypton, the presently available experimental values are flawed.

Insertion of noble-gas atom (Kr and Xe) into noble-metal molecules (AuF and AuOH): Are they stable?

The structure and the stability of a new class of insertion compounds of noble-gas atoms of the type AuNgX (Ng=Kr, Xe and X=F, OH) have been investigated theoretically through ab initio molecular-orbital calculations. All the species are found to have a linear structure with a noble-gas-noble-metal bond, the distance of which is comparable to covalent bond length except the AuKrOH system, for which it lies in between the covalent and van der Waals limits. The dissociation energies corresponding to the lowest-energy fragmentation products, AuX+Ng have been computed to be -166.2, -276.0, -194.4, and -257.6 kJ/mol for AuXeF, AuKrF, AuXeOH, and AuKrOH, respectively, at the MP2 level of theory. The respective barrier heights corresponding to the bent transition states (Au-Ng-X bending mode) have been calculated to be 119.1, 74.9, 160.7, and 141.6 kJ/mol. However, three of these species are found to be metastable in their respective potential-energy surface, and the dissociation energies corresponding to the Au+Ng+X fragments have been calculated to be 112.9, 3.0, and 18.7 kJ/mol for AuXeF, AuKrF, and AuXeOH, respectively, at the same level of theory. An analysis of the nature of interactions involved in the Au-Ng-X systems has been performed using Bader's topological theory of atoms-in-molecules (AIM). Geometric as well as energetic considerations along with AIM results suggest a partial covalent nature of Au-Ng bonds in these systems. This work might have important implications in the preparation of a new class of insertion compounds of noble-gas atoms containing noble-gas-noble-metal bond.

Plasma Line Emission during Single-Bubble Cavitation

Emission lines from transitions between high-energy states of noble-gas atoms (Ne, Ar, Kr, and Xe) and ions (Ar(+), Kr(+), and Xe(+)) formed and excited during single-bubble cavitation in sulfuric acid are reported. The excited states responsible for these emission lines range 8.3 eV (for Xe) to 37.1 eV (for Ar(+)) above the respective ground states. Observation of emission lines allows for identification of intracavity species responsible for light emission; the populated energy levels indicate the plasma generated during cavitation is comprised of highly energetic particles.

Ultrasoft X-Ray Bremsstrahlung Isochromatic Spectra from 300–2000 eV Electrons on Ar and Kr

For the first time the bremsstrahlung effect was studied experimentally in the spectral region of 6.5-10 nm with 300-2000 eV electron scattering on Ar and Kr atoms. The isochromatic curves displayed maxima at electron energies of approximately = 0.7 keV (Ar) and approximately =1 keV (Kr); their positions are almost independent of the radiation wavelength in the range studied. These experimental data cannot be treated in the framework of theory based on the first Born approximation. A phenomenological modification of the quasiclassical (soft-photon) approximation is proposed which gives a qualitative treatment of data.

All-electron quantum Monte Carlo calculations for the noble gas atoms He to Xe

We report all-electron variational and diffusion quantum Monte Carlo (VMC and DMC) calculations for the noble gas atoms He, Ne, Ar, Kr, and Xe. The calculations were performed using Slater-Jastrow wave functions with Hartree-Fock single-particle orbitals. The quality of both the optimized Jastrow factors and the nodal surfaces of the wave functions declines with increasing atomic number Z, but the DMC calculations are tractable and well behaved in all cases. We discuss the scaling of the computational cost of DMC calculations with Z.

Collision-induced nonadiabatic transitions in the second-tier ion-pair states of iodine molecule: Experimental and theoretical study of the I2(fg+) collisions with rare gas atoms

Nonadiabatic transitions induced by collisions with He, Ar, Kr, and Xe atoms in the I(2) molecule excited to the f0(g)(+) second-tier ion-pair state are investigated by means of the optical-optical double resonance spectroscopy. Fluorescence spectra reveal that the transition to the F0(u)(+) state is a dominant nonradiative decay channel for f state in He, Ar, and Kr, whereas the reactive quenching is more efficient for collisions with Xe atom. Total rate constants and vibrational product state distributions for the f-->F electronic energy transfer are determined and analyzed in terms of energy gaps and Franck-Condon factors for the combining vibronic levels at initial vibrational excitations v(f)=8, 10, 14, and 17. Quantum scattering calculations are performed for collisions with He and Ar atoms, implementing a combination of the diatomics-in-molecule and long-range perturbation theories to evaluate diabatic PESs and coupling matrix elements. Calculated rate constants and vibrational product state distributions agree well with the measured ones, especially in case of Ar. Qualitative comparison is made with the previous results for the second-tier f0(g)(+)-->F0(u)(+) transition in collisions with I(2)(X) molecule and the first-tier E0(g)(+)-->D0(u)(+) transition induced by collisions with the rare gas atoms.

Investigation of triply excited states of Li-like ions in fast ion-atom collisions by zero-degree Auger projectile electron spectroscopy

The production of triply excited states of Li-like systems has recently been extended beyond the lithium atom using two different ion-atom collisional techniques: (a) Triple-electron capture into 2s2p 2 and 2p 3 states of F 6+ formed in fast collisions of bare F 9+ ions with Ar and Kr atoms and (b) 180° resonant scattering of quasi-free electrons of H 2 from the 1s2s 3S metastable state of He-like B, C, N, O and F ions via the 2s2p 2 2D resonance. Autoionization energies, decay branching ratios and production cross sections for these states were measured using zero-degree Auger projectile electron spectroscopy and compared to theoretical calculations using hyperspherical close coupling (HSCC) and R-matrix methods.

Molecular dynamics study of the sputtering of Al cluster by Ar and Kr atoms

The numerical studies of the dynamics of the crystaline lattice formed by atoms requires the detailed knowledge of the forces between these atoms. In our contribution we concentrate on molecular dynamics study of sputtering of Al cluster in the form of the cube (i.e. eight Al atoms). The sputtering is due to impact of Ar and Kr atoms of energy 550 eV. We compare the use of the potential between atoms either of Moliere type or the embedded atom potential which has been proposed recently. For the choice of both potential the spectra of sputtered particles were calulated and the comparison was made.

Radioactive krypton background evaluation using atom counting

The beta-decay of 85Kr is a significant radioactive background for experiments that use liquified noble gases to search for dark matter and measure the low-energy solar neutrino flux. While there are several proposed methods for reducing Kr levels in these experiments, an independent technique is needed for measuring very low Kr levels. By selectively exciting Kr atoms to a metastable state, capturing them in a magneto-optical trap (MOT), and detecting fluorescence from the trapped atoms, individual Kr atoms can be counted with a high signal-to-noise ratio. This approach could be used to ascertain Kr impurity levels in other noble gases, with an estimated sensitivity of 3 × 10 - 14 .

Method of the reduced-added Green function in the calculation of atomic polarizabilities

The Green function in the quantum defect theory provides an exact account for high-excited and continuum electronic states. We modify it by taking into account the ground and low-excited states using their wave functions calculated ab initio. As an application, we present a simple and efficient semianalytical method for the calculation of atomic electric frequency-dependent scalar dipole polarizability, for both real and imaginary frequencies. The polarizabilities calculated for some atoms (Li, Na, K, Be, Mg, Ca, Si, P, S, O, Al, Ge, C, N, F, He, Ne, Ar, Kr, and Xe) are compared with existing methods of computational quantum chemistry and with experiments; good accuracy of the proposed method is demonstrated.

Dependence upon the molecular and atomic ground state of higher-order harmonic generation in the few-optical-cycle regime

High-order harmonic generation from molecules (${\mathrm{O}}_{2}$, ${\mathrm{N}}_{2}$, ${\mathrm{H}}_{2}$, and $\mathrm{C}{\mathrm{O}}_{2}$) and atoms (Xe, Ar, and Kr) has been studied in the few optical cycle domain. Two laser peak intensities; $2\ifmmode\times\else\texttimes\fi{}{10}^{14}$ and $6\ifmmode\times\else\texttimes\fi{}{10}^{14}\phantom{\rule{0.3em}{0ex}}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$, were compared. At the lower intensity spectra were approximately the same for molecules and atoms with the same ionization potential, at higher laser intensity the cutoff of ${\mathrm{O}}_{2}$ and $\mathrm{C}{\mathrm{O}}_{2}$ extends far beyond the cutoff of Xe and Kr, respectively, in contrast with ${\mathrm{N}}_{2}$ and ${\mathrm{H}}_{2}$ which exhibit cutoffs very close to that of Ar. This behavior is well explained by adopting an atomlike approximation for the molecule response in the high-field regime and employing the Lewenstein's model, properly modified in order to account for the nonlinear dipole moment of a randomly oriented molecule ensemble.

Calculation and Simulation of Absorption Line Broadening in Water Vapor by Noble Gas Atoms

Semiclassical methods have been applied to calculate the collisional broadening of water vapor absorption lines by noble gas atoms (Ar, He, Ne, and Kr). An analytical model has been proposed for line half-widths. The model parameters have been determined for the ν2 band of the H2O molecule for all the buffer gases under consideration, as well as for the bands 3ν1 + ν3 and 2ν1 + 2ν2 + ν3 in the case of the broadening by argon. In the latter case, the model parameters that determine the temperature dependence of the half-widths of the water vapor lines of the ν2 band have been found. The model proposed describes well the known experimental data and permits a relatively simple calculation of the H2O line half-widths for the bands and the buffer gases under consideration in a wide range of rotational quantum numbers. For the ν2 band, the model calculations in the case of the broadening by argon can be performed up to temperatures of 2500 K.

Theoretical study of chemical compounds formed by insertion of rare gas atoms into glycine molecule: a step towards bio-rare gas chemistry?

Stability, structural and vibrational properties of compounds where an Rg atom (Xe, Kr, or Ar) is inserted into different bonds of glycine molecule are investigated using accurate ab initio methods. The most stable configuration is found to correspond to insertion of Rg atoms into the O H bond of glycine. These NH 2CH 2COORgH compounds are metastable, but separated from the Rg + glycine dissociation products by significant potential barriers. Preliminary calculations show that NH 2CH 2COOXeH compound may be energetically stable with respect to the three-body dissociation (H + Rg + NH 2CH 2CO 2), while the corresponding Ar compound is energetically unstable in this respect. The compound with the inserted Kr is a borderline case, with the three-body dissociation products close in energy to the NH 2CH 2COOKrH minimum.

On the Delocalization of Electrons in Atoms and Molecules

A quantitative measure of the delocalization of electrons from the region inside a sphere of radius R centered on a nucleus to the region exterior to this sphere is the atom delocalization index A(R). A(R) is defined by the double integral of the point-point sharing index I(ζ;ζ') over two distinct volumes: ζ over the interior of a sphere of radius R, and ζ' over the remaining space. This index, as a function of R, has a remarkable shell-like structure with the values of the maxima being close to the number of electrons traditionally assigned to a particular shell times 0.25. The origin of these almost magic numbers and the reasons for deviations of these numbers from the simple rule is discussed in terms of simple models of the electronic structure of some light atoms. Results from numerical computations of electronic structure are presented for the atoms Li, Be, Al, Ne, Ar, Kr, Xe, Rn, Zn, and Au. The distinct shell-like structure of A(R) persists even to the heaviest of these. For atoms with zero total orbital angular momentum, the delocalization index can be split into a sum of noninterfering terms of different single particle angular momenta. These contributions also have distinctive shell-like structures. The maxima of the different angular momentum contributions do not always coincide. A similar decomposition also holds for spin up and down contributions. The shell-like structure allows for the identification of the spatial region in which the valence electrons lie. The angular momentum contributions can be used to identify the nature of the valence regions. The invariance of the core electron regions and the changes in the valence regions upon bond formation are illustrated by the calculation of the delocalization index for the heavy atoms in CH 4 , NH 3 , H 2 O, and SiH 4 . The identification of the spatial location of the valence regions should aid choosing the location of fixed points when analyzing the behavior of electrons using sharing amplitudes.

Hartree‐Fock‐Roothaan calculations for ground states of some atoms using minimal basis sets of integer and noninteger n‐STOs

AbstractHartree‐Fock‐Roothaan (HFR) calculations for ground states of some atoms, i.e. He, Be, Ne, Ar, and Kr have been performed using minimal basis sets of Slater type orbitals (STOs) with integer and noninteger principal quantum numbers (integer n‐STOs and noninteger n‐STOs). The obtained total energies for these atoms using minimal basis sets of integer n‐STOs are in good agreement with those in the previous literature. On the other hand, for the case of minimal basis sets of noninteger n‐STOs, although the calculated total energies of these atoms agree well with the results in Literature, some striking results have been obtained for atoms Ar and Kr. Our computational results for the energies of atoms Ar and Kr are slightly better than those in literature. by amount of 0.00222 and 0.000054 a.u., respectively. The improvement in the energies of atoms Ar and Kr may result from the efficient calculations of one‐center two‐electron integrals over noninteger n‐STOs. For some atomic ions in their ground state, HFR calculations have been carried out using minimal basis sets of noninteger n‐STOs. The obtained total energies for these atomic ions are substantially lower than those available in literature.

“Eclipse” Effect in the Scattering of Weakly Bound Helium Clusters

The total cross sections of the helium dimer, trimer, and tetramer for scattering from Kr atoms have been measured for cluster beam velocities between 250 and 820 m/s. The dimer cross section is twice that of the atom within 5% indicating that the Kr atoms scatter from the He atoms independently, which is consistent with the large dimer bond distance of about 50 A. The trimer and tetramer cross sections are somewhat larger and can be described by an impulse approximation with a multiple "eclipse" correction, extending ideas of Glauber for high energy collisions with the deuteron.