Noble Gas Atoms Research Articles

Prediction of pressure-induced stabilization of noble-gas-atom compounds with alkali oxides and alkali sulfides

The cubic antifluorite structure comprises a fcc sublattice of anions with cations on the tetrahedral sites. The voids in the antifluorite structure that are crucial for superionicity in ${\mathrm{Li}}_{2}\mathrm{O}$ might also act as atomic traps. Trapping of guest atoms and small molecules within voids of a host structure leads to the formation of what are known as clathrate compounds. Here we investigate the possibility of trapping helium or larger neon guest atoms under pressure within alkali-metal oxide and sulfide structures. We find stable helium and neon-bearing compounds at very low pressures. These structures are stabilized by a reduction in volume from incorporation of helium or neon atoms within the antifluorite structure. We predict that ${\mathrm{NeCs}}_{2}\mathrm{S}$ could be stable at ambient pressure. Our study suggests a novel class of alkali oxide and sulfide materials incorporating noble-gas atoms that might potentially be useful for gas storage.

Quantum chemical prediction of a superelectrophilic dianion and its binding with noble gas atoms.

The present communication shows an unprecedented superelectrophilic behaviour of dianion [BeB11(CN)11]2-, containing a positively charged electrophilic center embedded in a negatively charged framework. This dianion is shown to form stable [NgBeB11(CN)11]2- (Ng = He, Ne, Ar, Kr and Xe) compounds associated with either a Ng-Be or Ng-B bond. The dianion [BeB11(CN)11]2- binds covalently with Ar, Kr and Xe via its uncoordinated B atom.

Insight into the halogen-bond nature of noble gas-chlorine systems by molecular beam scattering experiments, ab initio calculations and charge displacement analysis.

We have carried out molecular-beam scattering experiments and high-level ab initio investigations on the potential energy surfaces of a series of noble-gas-Cl2 adducts. This effort has permitted the construction of a simple, reliable and easily generalizable analytical model potential formulation, which is based on a few physically meaningful parameters of the interacting partners and transparently shows the origin, strength, and stereospecificity of the various interaction components. The results demonstrate quantitatively beyond doubt that the interaction between a noble-gas (Ng) atom - even He - and Cl2 in a collinear configuration is characterized by weak halogen bond (XB) formation, accompanied by charge transfer (CT) from the Ng to chlorine. This characteristic, which stabilizes the adduct, rapidly disappears on going towards the T-shaped configuration, dominated by pure van der Waals (vdW) forces. Similarly, a pure vdW interaction takes place - with no CT component in any configuration - if Cl2 is present in the lowest πg* → σu* excited state, because the change in electron density that accompanies the excitation eliminates the Cl2 polar flattening and σ hole, making the XB interaction inaccessible.

Relative extent of triple Auger decay in CO and CO2.

Systematic measurements on single and triple Auger decay in CO and CO2 after the creation of a C 1s or a O 1s core vacancy show that the percentage of triple Auger decay is on the order of 10-2 of the single Auger decay in these molecules. The fractions of triple Auger decay are compared with triple Auger fractions for carbon atoms and some noble gas atoms, and are found to follow a linear trend correlated to the number of valence electrons on the atom with the initial core vacancy and on its closest neighbours. This linear trend for the percentage of triple Auger decay is represented by a predictive equation TA = 0.13·Nve - 0.5.

A Novel Metastable Atom Source Based on DC Glow Discharge Pinch

− Metastable atoms of noble gases have many applications in scientific research and industrial application. Though previously many such development of metastable atom sources are reported, in our endeavor for development of a source of this kind, we could develop a novel, simple structure, maintenance free glow discharge source that could produce metastable atoms of noble gases. This source is devised with two cathodes and a cylindrical anode paired with one permanent magnet. The electric field in between cathodes and the anode coupled with the magnetic field produce glow discharge in the centre of the source. The device was tested for various combination of anode voltage and filled helium pressure. The anode voltage was varied from 300 to 2000 V where as the filled pressure was varied from 450 mTorr to 1 Torr. The plasma extends to the outside of the source volume through the aperture in one of the cathode in form of a pinched glow. Due to this pinch, energetic electrons are generated and they excite the neutral atoms in their vicinity. The spectral lines of the glow discharge were observed by one optical spectrometer. Metastable helium atoms were observed at their transition wavelengths of 388.8 and 501.6 nm. The detail designing of the source and experimental results are reported in this article.

Noble gas dimers confined inside C70.

The potential energy surfaces for the interior rotation of a series of pairs of noble gas atoms encapsulated in the C70 cavity have been explored. He2@C70, Ne2@C70, Ar2@C70, HeNe@C70, HeAr@C70 and NeAr@C70 were chosen as case studies. Our calculations suggest stable minima with the two noble gas atoms lying along the symmetry axis of the fullerene. Transition states for the rotations are expected to occur when the two atoms are located in the symmetry plane perpendicular to the C5 axis. The energy barriers for the rotations are predicted to be in the 5-64 kcal mol-1 range, significantly increasing with the size of the noble gas atoms inside C70. These energy barriers lead to a wide range of rate constants, including those characteristic of very fast internal rotations, of the order of k = 2.40 × 109 s-1 for He2@C70, and those describing very slow rotations, of the order of k = 1.80 × 10-33 s-1 for Ar2@C70. It is mandatory to correct for the basis set superposition error to calculate accurate binding energies.

Noble Gas-Tungsten Peroxide Complexes in Noble Gas Matrixes: Infrared Spectroscopy and Density Functional Theoretical Study.

The matrix isolation infrared spectroscopic and quantum chemical calculation results indicate that tungsten oxo and mono-superoxide, WO3 and (η2-O2)WO2, coordinate noble gas atoms in forming noble gas-tungsten oxide complexes. The results showed that both WO3 and (η2-O2)WO2 oxides can coordinate one Ar or Xe atom in solid noble gas matrixes; otherwise, tungsten mono- and dioxides cannot. Hence, the WO3 and (η2-O2)WO2 molecules trapped previously in solid argon noble gas matrixes should be regarded as the WO3(Ar) oxide and (η2-O2)WO2(Ar) peroxide complexes. When annealing, the lighter Ar atom can be replaced by a heavier xenon atom to form WO3(Xe) and (η2-O2)WO2(Xe) complexes. What's more, upon UV photolysis, both Ar and Xe atoms can be replaced by oxygen to form a tungsten disuperoxide (η2-O2)2WO2 complex. The binding energies were predicted to be 25.7, 16.6, 9.4, 14.7, and 8.1 kcal/mol for the (η2-O2)2WO2, WO3(Xe), WO3(Ar), (η2-O2)WO2(Xe), and (η2-O2)WO2(Ar) complexes at the CCSD(T)//M06-2X-D3//def2-TZVP/DGDZVP/SDD level. The substitution law, O2 > Xe > Ar, can be interpreted according to the chemical reaction energies calculated to be -6.6 and +11.0 kcal/mol, respectively, for the equation formulas Xe + (η2-O2)WO2(Ar) = (η2-O2)WO2(Xe) + Ar and O2 + (η2-O2)WO2(Xe) = (η2-O2)2WO2 + Xe at the same level.

Dispersion-corrected PBEsol exchange-correlation functional

We study the compatibility between the PBEsol exchange-correlation energy functional of Phys. Rev. Lett. 100, 136406 (2008) and the rVV10 van der Waals nonlocal correlation functional of Phys. Rev. B 87, 041108 (2013). By applying a density-gradient dependence in the expression of rVV10, we develop a new functional: The PBEsol + rVV10s functional, which is remarkably accurate for layered solids, rare-gas crystals, densely packed bulk solids, and the adsorption of noble-gas atoms on metal surfaces, and is also competitive for noncovalent interactions between molecular complexes as well as for potential-energy curves of noble-gas dimers. The capacity of this dispersion-corrected functional to describe various interactions in solids makes it useful for electronic-structure calculations in solid-state physics and materials science.

Molecular Dynamics Simulations of Noble Gas Fractionation during Diffusion through Silica Nanopores

Ne retention and slight enrichment of Kr–Xe relative to atmospheric levels have been found in biogenic chert samples. Previous studies suggested that the incorporation of noble gas atoms is dependent upon the structure rather than the environment. In this study, we perform molecular dynamics simulations of dissolved noble gas atomic diffusion through 1–4 nm diameter silica pores. Bulk-liquid-like water does not exist in the 1 nm diameter nanopores, which hinder noble gas diffusion into or out of the pores. In ≥2 nm diameter nanopores, noble gas atoms transport with bulk-liquid-like water into the center of the pores but size-controlled diffusive separation occurs at the layer of surface water and in the interior of the silica structure. The motion of large atoms (Kr and Xe) in surface water is governed by significant adsorption. Relatively small Ne atoms are able to cross the surface water layer and diffuse into the crystal interior. As a result of its moderate size and the negligible interaction with the interfacial surface, Ar lies beyond the adsorption and silica structure diffusion regimes. Therefore, our simulation results indicate that noble gas entrapment is expected to occur in nanoscale fluid circulation during sediment-to-chert lithification.

H2+ MOLEKÜLÜNÜN DÖNME ENERJİLERİNİN Ne + H2+  NeH+ + H REAKSİYONU ÜZERİNDEKİ ETKİSİ

The noble gas atoms such as He, Ne and Ar have significantly electronic ionization values around liquid nitrogen temperature (at low temperature values). Because of this feature, the noble gases which are used for some gas detectors, and which is related certain chemical process occurring in the low temperature regions of atmosphere are encouraged to be researched. The chemical reactions subjected to these noble gas atoms have been believed to exhibit important behaviors at the same temperature values. The investigation of their quantum effects in particular energy range and the dependence on temperature of chemical reactions consisting of atom-diatom molecular systems include the subject of reaction dynamics. The title reaction has showed stable structure feature in the interaction region which is the nearest inter-atomic distance. For this reason, it causes to be examined of dynamic effects by depending on quantum states of initial hydrogen ion. The contributions of angular behaviors of hydrogen ion related to total angular momentum and the effects of these behaviors to reaction formations are examined via three dimensional quantum mechanical methods.

Coulomb potential effects in strong-field atomic ionization under elliptical polarization

We experimentally and theoretically investigate strong-field ionization of noble-gas atoms in elliptically polarized laser fields at 2000 nm. The ellipticity dependence of the ion yields has been measured at a series of intensities and compared to various theoretical model predictions [i.e., the Ammosov-Delone-Krainov (ADK), strong-field approximation (SFA), and Coulomb-Volkov distorted-wave approximation (CVA) models]. The SFA and ADK calculations match each other, which alludes to the negligible contribution of nonadiabatic effect. In the meantime, they both deviate significantly from the measurements. On the other hand, the good agreement between CVA calculations and measurements reveals the salient role played by the Coulomb potential in atomic ionization. The Coulomb potential effect is further confirmed by comparison of CVA calculations and measurements at 800 nm. Our work demonstrates the significant Coulomb potential effect on the ionization yields, the experimental evidence of which has rarely been documented.

Elastic Scattering of Ultrashort Laser Pulses on Noble Gas Atoms

The work deals with a theoretical investigation of elastic scattering of ultrashort electromagnetic pulses (USP) on the noble gas atoms in the far ultra-violet and soft X-ray regions. The investigation is performed within the framework of a dipole approximation and the first-order quantum-mechanics perturbation theory. Major attention is given to the study of the dependence of the total probability of scattering within the pulse time on the USP duration at different carrying frequency values. It is shown that at certain values of the problem parameters this dependence is nonlinear. The calculations are performed for the corrected Gaussian pulses and wavelet pulses without the carrying frequency.

Noble gas inserted compounds of borazine and its derivative B3N3R6: structures and bonding.

Quantum chemistry computations were performed at the MP2 and B3LYP levels of theory using the basis sets aug-cc-pVDZ and def2-TZVPPD to study the noble gas (Ng) compounds formed by insertion of a Ng atom (Kr, Xe, Rn) into the B-H/F and N-H/F bonds of inorganic benzene B3N3H6 and its fluorine derivative B3N3F6. The geometrical structures were optimized and vibrational analysis was carried out to demonstrate these structures being local minima on the potential energy surface. The thermodynamic properties of the formation process of Ng compounds were calculated. A series of theoretical methods based on the wavefunction analysis, including NBO, AIM and ELF methods and energy decomposition analysis, was used to investigate the bonding nature of the noble gas atoms and the properties of the Ng compounds. The N-Ng bond was found to be stronger than the B-Ng bond, but the B-Ng bond is of typical covalent character and σ-donation from the Ng atom to the ring B atom makes the predominant contribution towards stability of the B-Ng bond. NICS calculation shows that these Ng-containing compounds are of weak π-aromaticity.

On the separation of the information content of the Fermi and Coulomb holes and their influence on the electronic properties of molecular systems

ABSTRACTIn this paper, two information-based functions are employed as a real space measure of the Fermi and Coulomb holes for same-spin electrons. The first one is the information content of the Exchange-Correlation hole, calculated from the Kullback–Leibler divergence of the same-spin conditional pair density respect to the marginal probability (). As reported previously, , can be used to reveal the regions of the space associated to the classical electron pair model. Here, correlated wave-functions, such as CISD, MP2, and CCSD, are considered for the calculation of . This is achieved by introducing an approximated method based on employing natural orbitals and their occupancy numbers. In addition to , in this work we propose a measure of the information content of the same-spin correlation hole, which is computed in terms of the Kullback–Leibler divergence of a correlated same-spin conditional pair density respect to the uncorrelated Hartree–Fock pair density (). The proposed methodology is discussed in the light of the result derived from noble gas atoms, the molecule and some non-covalently bonded systems.

Screening of an oscillating external electric field in atoms

We study the screening of a homogeneous oscillating external electric field $E_0$ in noble-gas atoms using atomic many-body calculations. At zero frequency of the oscillations ($\omega=0$) the screened field $E(r)$ vanishes at the nucleus, $E(0)=0$. However, the profile of the field $E(r)$ is complicated, with the magnitude of the field exceeding the external field $E_0$ at certain points. For $\omega >0$ the field $E(r,\omega)$ strongly depends on $\omega$ and at some points may exceed the external field $E_0$ many times. The field at the nucleus is not totally screened and grows with $\omega$ faster than $\omega^2$. It can even be enhanced when $\omega$ comes close to resonance with a frequency of an atomic transition. This field interacts with CP-violating nuclear electric dipole moments creating new opportunities for studying them. The screening of the external field by atomic electrons may strongly suppress (or enhance near an atomic resonance) the low energy nuclear electric dipole transitions.

Dissolved state of radon with cluster molecules of solvent

Radon has been known to dissolve well in water although the exact mechanism of this process is still not clear. Thus we investigate a correlation of the solubility of radon to solvent clusters. We found experimentally that the solubility decreases in ethanol–water solutions at certain ethanol contents. Calculation of the clathration enthalpies for a noble gas atom confined in (H2O)20 clusters were performed by using a DFT method to find a correlation between the theoretical enthalpies and experimental enthalpies of dissolution. It is suggested from the results that radon is water-soluble due to encapsulation in a water cluster.

Intershell-correlation-induced time delay in atomic photoionization

We predict an observable Wigner time delay in outer atomic shell photoionization near inner shell thresholds. The near-threshold increase of time delay is caused by intershell correlation and serves as a sensitive probe of this effect. The time delay increase is present even when the inner and outer shell thresholds are hundreds of electron volts apart. We illustrate this observation by several prototypical examples in noble gas atoms from Ne to Kr. In our study, we employ the random phase approximation with exchange and its relativistic generalization. We also support our findings by a simplified, yet quite insightful, treatment within the lowest-order perturbation theory.

Dispersion and polar flattening: noble gas-halogen complexes.

High-level ab initio calculations on the complexes between noble gas atoms (He, Ne, Ar, Kr, and Xe) and dihalogen molecules (F2, Cl2, Br2, and I2) reveal trends, both in interaction energies and the energy difference between the linear and T-shaped structures, that can be explained well in terms of dispersion interactions enhanced by polar flattening of the halogens. The partial discrepancies with experimental findings are discussed. Graphical abstract The molecular electrostatic potential (red positive, blue negative) of Cl2...Br2 projected onto the 0.003 a.u. isodensity surface.

Simulation of angular-resolved RABBITT measurements in noble-gas atoms

We simulate angular resolved RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) measurements on valence shells of noble gas atoms (Ne, Ar, Kr, and Xe). Our non-perturbative numerical simulation is based on solution of the time-dependent Schr\"odinger equation for a target atom driven by an ionizing XUV and dressing IR fields. From these simulations we extract the angular dependent magnitude and phase of the RABBITT oscillations and deduce the corresponding angular anisotropy {\beta} parameter and Wigner time delay ${\tau}_W$ for the single XUV photon absorption which initiates the RABBITT process. Said {\beta} and ${\tau}_W$ parameters are compared with calculations in the random phase approximation with exchange (RPAE) which includes inter-shell correlation. This comparison is used to test various effective potentials employed in the one-electron TDSE. In lighter atoms (Ne and Ar), several effective potentials are found to provide accurate simulation of RABBITT measurements for a wide range of photon energies up to 100 eV above the valence shell threshold. In heavier atoms (Kr and Xe), the onset of strong correlation with the d-shell restricts the validity of the single active electron approximation to several tens of eV above the valence shell threshold.

What is the Smallest Atom as a Probe for Characterizing Nanostructures?

In gas adsorption techniques for characterizing the surface structure of solids and the porosity of porous materials, a smaller adsorptive is expected to be useful as a probe to detect finer structures. According to the periodic table, the smallest noble gas atom is helium. However, in cryogenic systems, light atoms such as helium behave as atoms larger than the size estimated from their electron shell structures because of the uncertainty in the position of the atom arising from quantum effects. Here, to unveil the smallest atom as a probe, we perform path integral grand canonical Monte Carlo simulations for the adsorption of noble gases on pore and solid surface models at the respective boiling temperature of each noble gas. First, we show that helium gas behaves exactly as an atom larger than its classically estimated size at low temperatures; in pores, however, it is smaller than in the bulk phase because quantum delocalization is suppressed by the pore walls and helium anomalously acts as a spheroidal atom in confined space. Second, a systematic comparison of the simulation results reveals that neon can enter an extremely small space helium is unable to enter, suggesting that the effective size of the atom at cryogenic temperatures is determined by the size of the electron cloud and wave nature of an atomic nucleus; consequently, neon is the smallest and most suitable noble gas as a probe to access more in-depth information on atomistic scale nanostructures.