Gas Atoms Research Articles

A Gravitational-like Relationship of Dispersion Interactions is Exhibited by 40 Pairs of Molecules and Noble Gas Atoms.

We present computational results of many-body dispersion (MBD) interactions for 40 pairs of molecular and atomic species: hydrocarbons, silanes, corresponding fluorinated derivatives, pairs which have multiple H---H contacts between the molecules, as well as pairs having π-π interactions, and pairs of noble gases. The calculations reveal that the MBD stabilization energy (EDISP,MBD) obeys a global relationship, which is gravitational-like. It is proportional to the product of the masses of the two molecules (M1M2) and inversely proportional to the corresponding distances between the molecular centers-of-mass (RCOM-COM) or the H---H distances of the atoms mediating the interactions of the two molecules (RH-H). This relationship reflects the interactions of instantaneous dipoles, which are formed by the ensemble of bonds/atoms in the interacting molecules. Using the D4-corrected dispersion energy (EDISP,D4), which accounts for three-body interactions, we find that the EDISP,MBD and EDISP,D4 data sets are strongly correlated. Based on valence-bond modeling, the dispersion interactions occur primarily due to the increased contributions of the oscillating-ionic VB structures which maintain favorable electrostatic interactions; the [Sub─C+:H-+H:C-─Sub] and [Sub─C:-+H -H:C+─Sub] structures; Sub symbolizes general residues. This augmented contribution is complemented by simultaneously diminished-weights of the destabilizing pair of structures, [Sub─C+:H--H:C+─Sub] and [Sub─:C- H++H:C-─Sub]. The local charges are propagated to the entire ensemble of bonds/atoms by partially charging the Sub residues, thus bringing about the "gravitational-like" dependence of dispersion.

Density functional theory investigation for noble gases adsorption on B3C2H5 structure

Quantum chemical calculations were performed to study the binding affinity of the B3C2H5 cluster with noble gases. The results indicate that noble gas atoms especially the heavier ones such as Xe and Kr can form stable complexes with this cluster. Detailed analysis of the interaction mechanism reveals that the noble gas atoms serve as donor fragments in the formation of Ng@B3C2H5, 2Ng@B3C2H5, and 3Ng@B3C2H5 donor–acceptor complexes.

Relativistic treatment of hole alignment in noble gas atoms

The development in attosecond physics allows for unprecedented control of atoms and molecules in the time domain. Here, ultrashort pulses are used to prepare atomic ions in specific magnetic states, which may be important for controlling charge migration in molecules. Our work fills the knowledge gap of relativistic hole alignment prepared by femtosecond and attosecond pulses. The research focuses on optimizing the central frequency and duration of pulses to exploit specific spectral features, such as Fano profiles, Cooper minima, and giant resonances. Simulations are performed using the Relativistic Time-Dependent Configuration-Interaction Singles method. Ultrafast hole alignment with large ratios (on the order of one hundred) is observed in the outer-shell hole of argon. An even larger alignment (on the order of one thousand) is observed in the inner-shell hole of xenon.

Influence of hydrocarbon environment on electrical characteristics of Ge-As-Se-S chalcogenide glass system

The effect of propane-butane gas mixture on volt-Ampere characteristic (VAX) of thin–layer sandwich structure Al-Ge33As17S35Se15-Te obtained by thermal evaporation method in vacuum was investigated. It has been established that under the influence of gas atoms, the oscillations observed in VAX gradually decrease and disappear. This result is explained by the accumulation of neutral gas atoms into lower atomar pores. It has been shown that neutral gas atoms collected in pores lead to weakening of thermal-field ionization processes of U--centers, and to increase the speed of periodic deflection of charge carriers by these centers, which leads to an increase in the resistance of the sample.

On the theory of the nucleation of gas bubbles at grain boundaries and incoherent inclusions

On the base of the critical analysis of two-dimensional models of the nucleation of gas filled bubbles at grain boundaries of helium-implanted specimens under the action of tensile stresses, a new model is developed within the framework of the Reiss theory of homogeneous nucleation in binary systems. This approach considers that gas bubbles are formed as a result of agglomeration in a binary system of vacancies and gas atoms at grain boundaries, avoiding significant simplifications of previous models based on the classical nucleation theory for single-component (unary) systems. The new model is extended to consider the nucleation of Xe bubbles at grain boundaries in UO2 under irradiation conditions and can be used for numerical analysis of experimental observations after the foreseen implementation in a fuel performance code. A similar approach can be applied to the nucleation and growth of gas bubbles on incoherent inclusions, such as those observed in irradiated ODS steels.

The role of irradiation-enhanced interstitial diffusion in over-pressurizing fission gas bubbles in UO2

Fission gas bubbles in UO2 nuclear fuel have been observed to exhibit pressures in excess of the equilibrium bubble pressure; however, the cause of bubble over-pressurization has not yet been demonstrated. The mechanical interaction between a bubble and the surrounding matrix or grain boundary depends on the internal pressure of the bubble and local stress state, such that over-pressurized bubbles are thought to be responsible for fragmentation and pulverization, when exposed to a temperature ramp. Here, we investigate the role of U interstitials, produced through irradiation, in over-pressurizing bubbles by using a combined molecular dynamics (MD) and cluster dynamics approach. Firstly, the energies for the capture of interstitials and vacancies by bubbles have been determined from MD as a function of the ratio of gas atoms to vacancies that make up the bubble. Secondly, these reaction energies have been implemented in the cluster dynamics code Centipede to predict bubble over-pressurization as a function of temperature for typical fission rates. It was found that there is a transition from low pressure bubbles (at high temperatures) to high pressure bubbles (at lower temperatures). The cause of this behavior was shown to be the creation of irradiation-induced interstitials that are highly mobile relative to vacancies at low temperature; whereas, vacancies are sufficiently mobile at high temperatures to limit bubble pressures. This result supports the hypothesis that over-pressurized bubbles form during steady-state operation and that this behavior is highly sensitive to the local pellet temperature.

A multi-level-variable correlated mechanistic model system for irradiation-induced multi-scale volume growths of U-10Mo/Zr dispersion nuclear fuels

Irradiation-induced volumetric deformations in dispersion nuclear fuels arouse a critical concern in nuclear fuel design. Utilizing the concepts from mesomechanics and homogenization, a multi-level-variable correlated mechanistic model system called the Dispersion Fuel Swelling Analysis Model System (DFSAMS) is developed for the irradiation-induced multi-scale volume growths of U-10Mo/Zr dispersion nuclear fuels. These models could directly correlate the macroscopic irradiation-induced volume growth strain with the dynamically varying multi-level information, including the obtained particle volume fractions, the current porosities of recrystallized zones of fuel grains, the macroscale porosities of fuel particles, the average numbers of fission gas atoms within fuel bubbles, the average bubble pressures and the macroscale pressures of fuel particles related to the macroscale hydrostatic pressures of dispersion fuels. The obtained theoretical results align favorably with finite element predictions and a diverse range of experimental data, demonstrating the effectiveness of the newly developed model system. It is indicated that: (1) the irradiation creep performance of the Zr matrix becomes the predominant factor influencing the macroscale volume growth deformations of U-10Mo/Zr dispersion fuels, due to the differed resistance to volumetric deformations of U-10Mo particles; (2) the as-fabricated bubbles of fuel particles will gradually decrease in size under the macroscale hydrostatic pressures due to the irradiation creep deformations occurring in the surrounding solid skeleton, contributing negatively to the macroscale volumetric expansion of U-10Mo/Zr dispersion fuels, especially in cases with higher initial porosity. The important theoretical models are supplied here for efficient numerical simulation of the irradiation-induced thermal-mechanical coupling behaviors in U-10Mo/Zr dispersion fuel elements.

Rydberg-State Double-Well Potentials of Van der Waals Molecules

Recent progress in studies of Rydberg double-well electronic energy states of MeNg (Me = 12-group atom, Ng = noble gas atom) van der Waals (vdW) molecules is presented and analysed. The presentation covers approaches in experimental studies as well as ab initio-calculations of potential energy curves (PECs). The analysis is shown in a broader context of Rydberg states of hetero- and homo-diatomic molecules with PECs possessing complex ‘exotic’ structure. Laser induced fluorescence (LIF) excitation spectra and dispersed emission spectra employed in the spectroscopical characterization of Rydberg states are presented on the background of the diverse spectroscopic methods for their investigations such as laser vaporization–optical resonance (LV-OR), pump-and-probe methods, and polarization labelling spectroscopy. Important and current state-of-the-art applications of Rydberg states with irregular potentials in photoassociation (PA), vibrational and rotational cooling, molecular clocks, frequency standards, and molecular wave-packet interferometry are highlighted.

Two-phase modelling for fission gas sweeping in restructuring nuclear oxide fuel

In this work, we propose a modelling approach for the intra-granular fission gas behaviour in UO2 under restructuring process. Leveraging the definition of restructured volume fraction, we consider the fuel matrix transition from the non-restructured to the restructured phase, together with the evolution of the corresponding fission gas concentrations retained in the fuel matrix. Firstly, we derive a sweeping term that exchanges fission gas atoms from the non-restructured to the restructured fuel region. The sweeping term is then included in the conventional intra-granular fission gas diffusion problem. Secondly, the spectral diffusion algorithm is employed to solve two spatially-dimensionless problems, properly representing the non-restructured region with micrometric grains and the restructured region with sub-micrometric grains. The model developed is implemented in SCIANTIX, a 0D meso-scale code for physics-based modelling of fission gas behaviour in nuclear oxide fuel and compared with experimental data and semi-empirical models.

Predicting Collision-Induced-Dissociation Tandem Mass Spectra (CID-MS/MS) Using Ab Initio Molecular Dynamics.

Compound identification is at the center of metabolomics, usually by comparing experimental mass spectra against library spectra. However, most compounds are not commercially available to generate library spectra. Hence, for such compounds, MS/MS spectra need to be predicted. Machine learning and heuristic models have largely failed except for lipids. Here, quantum chemistry software can be used to predict mass spectra. However, quantum chemistry predictions for collision induced dissociation (CID) mass spectra in LC-MS/MS are rare. We present the CIDMD (Collision-Induced Dissociation via Molecular Dynamics) framework to model CID-based MS/MS spectra. It uses first-principles molecular dynamics (MD) to simulate the physical process of molecular collisions in CID tandem mass spectrometry. First, molecular ions are constructed at specific protonation sites. Using density functional theory, these protonated ions are targeted by argon collider gas atoms at user-specified velocities. Subsequent bond breakages are simulated over time for at least 1,000 fs. Each simulation is repeated multiple times from various collisional directions. Fragmentations are accumulated over those repeated collisions to generate CIDMD in silico mass spectra. Twelve small metabolites (<205 Da) were selected to test the accuracy of this framework in comparison to experimental MS/MS spectra. When testing different protomers, collider velocities, number of simulations, simulation time and impact factor b cutoffs, we yielded 261 predicted mass spectra. These in silico spectra resulted in entropy similarity scores of an average 624 ± 189 for all 261 spectra compared to their corresponding experimental spectra, which improved to 828 ± 77 when using optimal parameters of the most probable protomers for 12 molecules. With increasing molecular mass, higher velocities achieved better results. Similarly, different protomers showed large differences in fragmentation; hence, with increasing numbers of protomers and tautomers, the average CIDMD prediction accuracy decreased. Mechanistic details showed that specific fragment ions can be produced from different protomers via multiple fragmentation pathways. We propose that CIDMD is a suitable tool to predict mass spectra of small metabolites like produced by the gut microbiome.

Role of field ionization in laser pulse evolution during interaction of long laser pulse with gaseous hydrogen atoms

Role of field ionization in laser pulse evolution during interaction of long laser pulse with gaseous hydrogen atoms

Nuclear-excited source of coherent and incoherent radiation with direct nuclear pumping

Uranium fission fragments, as well as the products of 3He(n,p)3H and 10B(n,α)7Li nuclear reactions were utilized in the nuclear reactor for gas ionization and excitation. However, the 6Li(n,α)3H nuclear reaction was less examined. The use of lithium-6 as a surface source of excitation of the gas medium, due to the long path length of tritium nuclei in the gas, allows to excite large volumes of gas as opposed to using 235U or 10B.While investigating the luminescence of noble gases in the core of the IVG.1M research reactor, we noted an appearance of alkali metal lines and a sharp increase in the intensity of these lines at temperatures above 570 K. It was determined that the population of levels of lithium atoms has practically no effect on the population of the 2p-levels of atoms of noble gases. The selectivity of p- and s-levels deactivation by lithium atoms implies the possibility of creating inversion of population at 2p-1s transitions of noble gas atoms. Successful experiments to study the luminescence of gases upon excitation by 6Li(n,α)3H nuclear reaction products allow us to proceed to experiments to achieve the laser action threshold and study the lasing characteristics of gas mixtures at the IGR pulsed nuclear reactor with thermal neutron flux density up to 7∙1016 n/cm2s. For this purpose, an experimental device designs were proposed to perform experiments on the IGR reactor. A step-by-step procedure of fabrication of a nuclear-excited source for excitation of gas mixtures is provided. The results of reactor experiments aimed at determining the spectral and temporal characteristics of optical radiation during excitation of gas mixtures by 6Li(n,α)3H nuclear reaction products are presented.

Enhanced image transmission via four-wave mixing with assisted spiral phase contrast in hot atoms

Due to the diffusion motion of gas atoms, the object contour after frequency conversion becomes blurred, and the edge information of the image is always lost. Here, with assisted spiral phase contrast (SPC) imaging, we propose a scheme to preserve object edge information and enhance image recognition via four-wave mixing (FWM) process. The experimental results show that the algorithm can improve the structural similarity (SSIM) of object contour and the whole similarity of image. This work may contribute to the improvement of image quality via frequency conversion in atomic ensembles, and provides a possible implementation in all-optical image processing.

An algorithm for very high pressure molecular dynamics simulations.

We describe a method to run simulations of ground or excited state dynamics under extremely high pressures. The method is based on the introduction of a fictitious ideal gas that exerts the required pressure on a molecular sample and is therefore called XP-GAS (eXtreme Pressure by Gas Atoms in a Sphere). The algorithm is most suitable for approximately spherical clusters of molecules described by quantum chemistry methods, Molecular Mechanics or mixed QM/MM approaches. We compare the results obtained by the algorithm here presented and by the XP-PCM approach, based on a continuum description of the environment. As a test case, we study the conformational dynamics of 1,3-butadiene either as an isolated molecule ("naked" butadiene) or embedded in a cluster of argon atoms, under pressures up to 15 GPa. Overall, our results show that the XP-GAS QM/MM simulation method is in good agreement with the XP-PCM QM/Continuum model (Cammi model) in describing the effect of the pressure on static properties as the equilibrium geometry of butadiene in the ground state. Furthermore, the comparison of XP-GAS simulations with naked butadiene and butadiene in argon shows the importance, for XP-GAS and related methods, of a realistic representation of the medium in modelling pressure effects.

Beyond Traditional Perovskites: Xenon's Influence on the Vibrational and Electronic Properties of K4Xe3O12

AbstractThe perovskite structure is one of the most fascinating configurations existing in nature, with its physical and chemical properties heavily influenced by the nature and oxidation states of cations, stoichiometry, and crystalline structure. Layered perovskite material K4Xe3O12, an interesting member of this family, possesses energetic properties that require detailed investigation. To establish the governing principles and quantify the observed behaviors, a detailed computational investigation is conducted into the electronic, vibrational, structural, and optical characteristics of K4Xe3O12, utilizing Density Functional Theory (DFT) calculations. The calculated elastic constants adhere to Born's criteria, affirming the mechanical stability of trigonal K4Xe3O12, with a bulk modulus (Bo) of ≈53.93 GPa. This low compressibility is intricately tied to its robust perovskite structure, featuring XeO6 octahedra sandwiched between XeO3 molecules. Precise determination of the valence‐conduction bandgap is crucial for understanding potential connections to the photodecomposition phenomenon. Using the Tran‐Blaha‐modified Becke‐Johnson (TB‐mB) potential alongside traditional generalized gradient approximation (GGA) approach, a bandgap of ≈1.32 eV is determined. Rapid fluctuations in optical properties also suggest a propensity for photodecomposition in the visible spectrum. The study provides critical insights into perovskite materials, especially those containing noble gas atoms, unveiling unique chemical and physical properties that open up new avenues for versatile applications across various fields.

Optical manipulations without light forces: deep superlattice for trapping and rotation of impurity particles in a buffer gas

We propose a scheme to obtain a deep optical superlattice (OSL) for resonant impurity particles in a buffer gas. In contrast to the well-known traditional methods of forming optical lattices (supelattices) that are based on the gradient force of radiation pressure, the presented scheme is based on the effect of a light induced drift (LID) in interfering light waves. The principle of its operation is based on the conception of so-called rectified forces induced by interfering bichromatic optical fields, which was developed earlier in the theory of resonant radiation-pressure forces. In the scheme under consideration, a deep OSL (with a period much larger than the optical wavelength) is formed due to the action of the effective rectified force on atomic particles which is proportional to the difference between the frequencies of transport collisions of excited and unexcited particles with buffer gas atoms.

Imaging Spin-Orbit Excitation of Yttrium through High-Energy Collisions with Rare Gas Atoms.

The energy required for spin-orbit excitation plays a critical role in understanding translational-to-electronic energy conversion, particularly in chemical reactions involving changes in spin states. This is particularly important for transition metal atoms possessing d-orbitals, which result in multiple spin-orbit split energy levels at low energies. The accurate identification and characterization of spin-orbit transitions in such species require advanced experimental techniques and theoretical support. In this study, the spin-orbit excited collisions of Y(2D3/2) with rare gas atoms Ne, Ar, and Kr leading to Y(2D5/2) were observed using laser-ablated crossed-beam and time-sliced ion velocity mapping imaging techniques. Through a comparison of the forward angular distributions of Y(2D3/2) to the backward and sideway scattering distributions of Y(2D5/2) from elastic and inelastic collisions of Y(2D) with rare gas atoms, this study reveals that the spin-orbit electronic excitation occurs with high collision energy and low impact parameters from backward and sideway collisions. The effectiveness of the spin-orbit excitation process is strongly dependent on the collision energy or temperature, suggesting that energy requirements of the process have to be considered in chemical reactions involving changes in spin states.

Parameterization of vacancy production rate in phase-field models of fission gas bubble evolution in nuclear fuel

Phase-field modeling has increasingly been used to study microstructural evolution in fission gas bubbles in nuclear fuel to improve understanding of fission gas release. To improve computational efficiency, often only vacancies and gas atoms are included as defect species. In this case, the net effects of vacancy and interstitial production, recombination, and biased sink absorption are included as a net vacancy source, or net vacancy source combined with an effective sink. However, there has been a lack of clarity on what parameter values should be used for these approaches to best match the more complete physical picture that includes interstitials and vacancies. Here, we compare a phase-field model of void growth to analytical models for the source-only and source plus sink approach to gain insight into how the phase-field models can be parameterized effectively. The source-only approach provides greater flexibility to match growth rates determined from the full vacancy-interstitial picture. A strategy was developed for determining the value of the net vacancy source term by comparing to an analytical model that includes vacancy and interstitial production, recombination, and biased sink absorption. This strategy can be used to parameterize phase-field models of fission gas bubble growth.

Determination of the polarization of Xe nuclear spin using transverse and longitudinal Rb in-situ magnetometers in NMR co-magnetometers

NMR co-magnetometers, as novel atomic sensors, can measure the angular velocity information in inertial measurements by detecting the spin precession of Xe nuclei. The Xe polarization plays a crucial role in the sensing unit of co-magnetometers, as it enhances the signal-to-noise ratio (SNR) and sensitivity of NMR sensors. Here we elucidated the Rabi dynamics of Xe nuclear spin and demonstrated two methods to determine the Xe polarization based on the classical Bloch equations. By detecting the optical rotation angle signal, we acquired the amplitude and the phase variations information in two methods, respectively. The transverse magnetometer relies on the amplitude of the free induction decay (FID) signal and applies a short pulse to flip the Xe fields into the transverse plane, enabling precise measurements. On the other hand, the longitudinal magnetometer offers an intuitive approach to measuring the demodulated phase variations by capturing the repetitive flips of longitudinal Xe fields. This paper discusses the advantages and disadvantages of both proposed methods, with the aim of enhancing the accuracy and authenticity of nuclear spin polarization measurements for noble gas atoms in atomic sensors.

Hyperdoping of germanium with argon toward strain-doping-induced indirect-to-direct bandgap transition in Ge

The first-principles calculations have recently shown that implanting sufficient noble gas atoms into germanium (Ge) can expand its lattice to achieve the desired tensile strain for indirect-to-direct bandgap transition to develop the on-chip high-efficient light emitter. Here, to experimentally prove this strain-doping concept, we implant argon (Ar) ions into Ge and then recrystallize the Ar-doped amorphous Ge (a-Ge) layer using nanosecond laser annealing (NLA) and furnace thermal annealing (FTA), respectively. The NLA effectively recrystallizes the 12 nm thick a-Ge layer with minimal loss of Ar dopants, while FTA fails to fully recrystallize it and results in significant loss of Ar dopants. The regrown Ge layer with Ar concentration above the critical value (0.8%) for bandgap transition is 3.8 nm thick, making it a challenge to distinguish the photoluminescence signal of strain-doped layer from the substrate. To overcome this, increasing the implantation energy and adding a capping layer may be necessary to further prevent Ar loss and achieve a strain-doped layer with sufficient depth. These findings provide promising view of the strain-doping concept for direct-bandgap emission from Ge.