Hot Atoms Research Articles

Desorption of hot deuterium atoms from the Pd/PdO:D x heterostructure under excitation of its hydrogen subsystem

Desorption of hot deuterium atoms from the Pd/PdO:D x heterostructure under excitation of its hydrogen subsystem

Hot atoms rotate light rapidly

The ability to harness the Faraday effect on a short timescale in an ensemble of hot atoms may prove useful as a read-out tool for quantum information based on microscale vapour cells.

Weakly bound buffer layers: A versatile template for metallic nano-clusters growth and film patterning on solid surfaces

Buffer layers composed of weakly bound atoms or molecules on solid surfaces are discussed as a versatile platform for size controlled growth of nano-clusters and for patterning of thin metallic films. Metallic nano-crystals can be prepared and their size and density be controlled by varying the film thickness. Cold metallic or oxide clusters, softly land and deposit on solid substrates via the Buffer Layer Assisted Growth (BLAG) method. Their final structure, therefore, reflects purely the interaction with the substrate with no kinetic constraints that may play a role in direct deposition methods of hot atoms. The nature of the buffer film, being a rare gas or a molecular film, can somewhat affect the shape of clusters as well. Applying laser ablation techniques, these weakly bound films were demonstrated to assist in patterning of metallic films. It operates on practically any cold, flat solid substrate that absorbs the laser light. Parallel stripes at sub-micron width, millimeter long, were obtained experimentally, with line width determined by the ablating laser power. The versatility of these weakly bound films in manipulating the structure of metallic particles and thin films is discussed in its wider potential scope.

Solar‐wind control of the hot oxygen corona around Mars

The global behavior and escape rate of hot oxygen atoms around Mars and their response to different solar wind dynamic pressure (PSW) conditions are investigated using a multidimensional time‐dependent magnetosheath‐ionosphere‐exosphere (Msh‐I‐E) coupling model. Recently we reported that an increase in PSW leads to a short‐term increase in the escape rate of nonthermal oxygen using a one‐dimensional (1‐D) Msh‐I‐E model. The model used in the present paper is a multidimensional version of our previous 1‐D model. For the exosphere model, we adopt a three‐dimensional Monte Carlo approach above a 250‐km altitude, while a time‐dependent two‐stream approach is employed below 250 km. The exosphere model is coupled with a two‐dimensional resistive magnetohydrodynamic model of the magnetosheath‐ionosphere interaction, assuming axial symmetry with respect to the Sun‐Mars line. The results of the present model are consistent with the results of the 1‐D model. The escape rate of hot oxygen for PSW = 0.36 nPa is roughly twice that for PSW = 1.43 nPa under steady state conditions. For nonstationary conditions, where PSW is suddenly increased from 0.36 to 1.43 nPa, the escape rate is temporarily enhanced by a factor of 2.3 to 4.5 compared with that of the steady state case. The hot oxygen density is found to be less dependent on PSW than is the escape rate.

Spatial Structure and Collisionless Electron Heating in Balmer‐dominated Shocks

Balmer-dominated shocks in supernova remnants (SNRs) produce strong hydrogen lines with a two-component profile composed of a narrow contribution from cold upstream hydrogen atoms and abroad contribution from hydrogen atoms that have undergone charge transfer reactions with hot protons. Observations of emission lines from edgewise shocks in SNRs can constrain the gas velocity and collisionless electron heating at the shock front. Downstream hydrogen atoms engage in charge transfer, excitation, and ionization reactions, defining an interaction region called the shock transition zone. The properties of hot hydrogen atoms produced by charge transfers (called broad neutrals) are critical for accurately calculating the structure and radiation from the shock transition zone. This paper is the third in a series describing the kinetic, fluid, and emission properties of Balmer-dominated shocks, and it is the first to properly treat the effect of broad neutral kinetics on the shock transition zone structure. We use our models to extract shock parameters from observations of Balmer-dominated SNRs. We find that the inferred shock velocities and electrontemperaturesarelower thanthoseof previouscalculations by 1500 km s � 1 . This effect is primarily due to the fact that excitation by proton collisions and charge transfer to excitedlevelsfavorthehigh-speedpartof theneutralhydrogenvelocitydistribution.Ourresultshaveastrongdependence on the ratio of the electron to proton temperatures, � � Te/Tp, which allows us to construct a relation � (vs) between the temperature ratio and the shock velocity.We compare our calculations to previous results byGhavamian and coworkers. Subject headingg shock waves — supernova remnants Online material: color figures

Impurity hot atoms in irradiated metals with different nuclear history

General relationships in the effect of the nuclear history on the forms of stabilization of impurity hot atoms and on the diffusion mobility and specific features of the physicochemical behavior of radioactive micro-impurities in the course of annealing of radiation-induced perturbations and of structural transformations of irradiated metals were elucidated. The forms of stabilization of impurity hot atoms in metals after irradiation and in the course of annealing of radiation-induced perturbations and of structural transformations, were determined by emission Mossbauer spectroscopy. It was shown that the positions occupied by impurity atoms in irradiated metals are determined by the nuclear history and crystallographic features of these metals. Studies of how impurity hot atoms formed by nuclear transformations migrate in the course of annealing of the irradiated metals show that the rate of migration of radioactive micro-impurities is determined by the extent of the radiation damage of the targets and by the possible position of the impurity hot or daughter atom in the crystal lattice of the irradiated metal. The transport mechanism accounting for the anomalous behavior of impurities is suggested. Anomalies (accelerated diffusion in the bulk and in surface layers of irradiated metals and emanation into the gas phase) in the physicochemical behavior of impurity atoms in the course of structural transformations of irradiated metals were revealed. These anomalies depend on the nuclear and mechanical history of the samples and on the conditions of their annealing. The interrelation between the nuclear history, crystallographic position of impurity hot atoms, their physicochemical characteristics, and structural changes occurring in metals in the course of irradiation, annealing of radiation-induced perturbations, and structural transformations was demonstrated by X-ray phase analysis and various kinds of Mossbauer spectroscopy. For metals having several allotropic modifications (Mn, Fe, Sn), the effect of stabilization of high- and low-temperature structural phases at room temperature upon irradiation was discovered.

Quantitation of the glycoprotein spike area on the surface of enveloped viruses

The density of glycoprotein (GP) distribution on the virion surface substantially influences the virus infectivity and pathogenicity. A method to quantitatively determine the area occupied by surface GP spikes was proposed for influenza virus (Flu) strain A/PR/8/34 on the basis of data of tritium bombardment and dynamic light scattering. The latter was used to measure the diameter of intact virions and subviral particles (Flu virions lacking GP spikes after bromelain digestion). Intact virions and subviral particles were bombarded with a hot tritium atom flux, and the specific radioactivity of the matrix M1 protein was analyzed. The tritium label was incorporated into the amino acid residues of a thin exposed protein layer and partly penetrated through the lipid bilayer of the viral envelope, labeling M1, located under the lipid bilayer. The tritium label distribution among different amino acid residues was the same in M1 isolated from subviral particles and M1 isolated from intact virions, demonstrating that the M1 spatial structure remained unchanged during proteolysis of GP spikes. The difference in specific radioactivity between the M1 proteins isolated from intact virions and subviral particles was used to calculate the GP-free portion of the viral surface. Approximating the Flu virion as a sphere, the GP-covered area was estimated at 1.4 × 104 nm2, about 40% of the total virion surface. This was consistent with the cryoelectron tomography data published for Flu strain A/X-31. The approach can be applied for other enveloped high pathogenic viruses, such as HIV and the Ebola virus.

Evidence of lasing without inversion in a hot rubidium vapor under electromagnetically-induced-transparency conditions

We report a likely observation of cw lasing without inversion in a gas of hot rubidium atoms in an optical cavity under conditions of electromagnetically induced transparency (EIT). The medium is pumped coherently and resonantly by a single ``coupling'' beam which also produces EIT in the lasing transition. The steady-state intensity exhibits thresholds as a function of the atomic density and the strength of the coupling beam. A theoretical model for an effective three-level lambda system indicates that gain without inversion is possible in this system if the two ground states are coupled by depolarizing collisions, and if the decay branching ratios meet certain conditions.

Consequences of the Heliopause Instability Caused by Charge Exchange

The heliopause (HP) is a tangential discontinuity that divides the interacting streams of the solar wind (SW) and local interstellar medium (LISM). It has been known for some time that the heliopause is subject to Rayleigh-Taylor instabilities driven and mediated byinterstellar neutralatoms. Here we identify anewform of instabilityontheflanks of HP driven by hot neutral hydrogen atoms created by charge exchange of interstellar neutrals with hot heliosheath plasma. To investigate the instabilities and the consequences of these on heliospheric structure we performed highresolution, shock-capturing, adaptive-mesh-refinementcalculations of the SW-LISMinteraction. Low numerical dissipation allows us to analyze the fine structure of the heliosheath resulting from the HP instability. We show that secondary neutrals play an essential role in destabilizing the flanks of the HP. We analyze the time-dependent location of the HP and the termination shock and the influence of their excursions on the plasma distribution in the inner heliosheath. It is found that perturbations generated by the HP instability can affect the distribution of plasma in the inner heliosheath on shorter timescales than the timescale of the instability as it develops near the stagnation axis. Finally, by way of application, we estimate the intensity of the soft X-ray emission generated in different regions of theHPandshowthatitsinstabilityleadstoasubstantialenhancementintheX-rayemissionwhichbearsanimprintof the HP shape. Subject headingg ISM: kinematics and dynamics — magnetic fields — MHD — shock waves — solar wind — X-rays: stars

Hyperthermal hydrogen atoms in argon-hydrogen atmospheric pressure microplasma jet

An argon-hydrogen atmospheric pressure microplasma jet was constructed for the treatment of materials. The microplasma jet device operating at 50 W produced long plasma jet of 30 mm with gas temperatures measured, using OH emissions, from 1600 to 2600 K as a function of distance. Excitation temperature was found to be from 7000 to 10 000 K. Through the analysis of Hα line broadening mechanisms, surprising hot hydrogen atoms H (n=3) were found with temperatures ranging from 12 000 to 19 600 K.

Impacts as sources of the exosphere on Mercury

Chemical processes associated with meteoroid bombardment of Mercury are considered. Meteoroid impacts lead to production of metal atoms as well as metal oxides and hydroxides in the planetary exosphere. By using quenching theory, the abundances of the main Na-, K-, Ca-, Fe-, Al-, Mg-, Si-, and Ti-containing species delivered to the exosphere during meteoroid impacts were estimated. Based on a correlation between the solar photo rates and the molecular constants of atmospheric diatomic molecules, photolysis lifetimes of metal oxides and SiO are estimated. Meteoroid impacts lead to the formation of hot metal atoms (0.2–0.4 eV) produced directly during impacts and of very hot metal atoms (1–2 eV) produced by the subsequent photolysis of oxides and hydroxides in the exosphere of Mercury. The concentrations of impact-produced atoms of the main elements in the exosphere are estimated relative to the observed concentrations of Ca, assumed to be produced mostly by ion sputtering. Condensation of dust grains can significantly reduce the concentrations of impact-produced atoms in the exosphere. Na, K, and Fe atoms are delivered to the exosphere directly by impacts while Ca, Al, Mg, Si, and Ti atoms are produced by the photolysis of their oxides and hydroxides. The chemistry of volatile elements such as H, S, C, and N during meteoroid bombardment is also considered. Our conclusions about the temperature and the concentrations of impact-produced atoms in the exosphere of Mercury may be checked by the Messenger spacecraft in the near future and by BepiColombo spacecraft some years later.

Simulation of dislocation-phonon interaction in metals

Motion of dislocations interacting with phonons has been simulated by means of molecular dynamics method. The embedded atom method potential for copper is adopted in the simulation. Model crystal is a rectangular solid containing about 140000 atoms. An edge dislocation is introduced along [112] direction near centre of model crystal, and the system is relaxed. After the dislocation configuration is stabilized, a shear stress is applied and released. Wavy motions of dislocations developed on the Peierls valleys are observed. Excitation of atoms consisting the dislocation by the propagation of 'hot atoms' is also observed in the simulation.

The loss of ions from Venus through the plasma wake

Venus, unlike Earth, is an extremely dry planet although both began with similar masses, distances from the Sun, and presumably water inventories. The high deuterium-to-hydrogen ratio in the venusian atmosphere relative to Earth's also indicates that the atmosphere has undergone significantly different evolution over the age of the Solar System. Present-day thermal escape is low for all atmospheric species. However, hydrogen can escape by means of collisions with hot atoms from ionospheric photochemistry, and although the bulk of O and O2 are gravitationally bound, heavy ions have been observed to escape through interaction with the solar wind. Nevertheless, their relative rates of escape, spatial distribution, and composition could not be determined from these previous measurements. Here we report Venus Express measurements showing that the dominant escaping ions are O+, He+ and H+. The escaping ions leave Venus through the plasma sheet (a central portion of the plasma wake) and in a boundary layer of the induced magnetosphere. The escape rate ratios are Q(H+)/Q(O+) = 1.9; Q(He+)/Q(O+) = 0.07. The first of these implies that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.

Fluorescence during Doppler cooling of a single trapped atom

We investigate the temporal dynamics of Doppler cooling of an initially hot single trapped atom in the weak-binding regime using a semiclassical approach. We develop an analytical model for the simplest case of a single vibrational mode for a harmonic trap, and show how this model allows us to estimate the initial energy of the trapped particle by observing the time-dependent fluorescence during the cooling process. The experimental implementation of this temperature measurement provides a way to measure atom heating rates by observing the temperature rise in the absence of cooling. This method is technically relatively simple compared to conventional sideband detection methods, and the two methods are in reasonable agreement. We also discuss the effects of rf micromotion, relevant for a trapped atomic ion, and the effect of coupling between the vibrational modes on the cooling dynamics.

Dynamical hole in ultrafast photoassociation: Analysis of the compression effect

Photoassociation of a pair of cold atoms by excitation with a short chirped laser pulse creates a dynamical hole in the initial continuum wave function. This hole is manifested by a void in the pair wave function and a momentum kick. Photoassociation into loosely bound levels of the external well in ${\mathrm{Cs}}_{2}\phantom{\rule{0.3em}{0ex}}{0}_{g}^{\ensuremath{-}}(6S+6{P}_{3∕2})$ is considered as a case study. After the pulse, the free evolution of the ground triplet state $a^{3}\ensuremath{\Sigma}_{u}^{+}$ wave packet is analyzed. Due to a negative momentum kick, motion to small distances is manifested and a compression effect is pointed out, markedly increasing the density of atom pairs at short distance. A consequence of the hole is the redistribution of the vibrational population in the $a^{3}\ensuremath{\Sigma}_{u}^{+}$ state, with population of the last bound level and creation of pairs of hot atoms. The physical interpretation makes use of the time dependence of the mass current and population on each channel to understand the role of the parameters of the photoassociation pulse. By varying such parameters, optimization of the compression effect in the ground-state wave packet is demonstrated. Due to an increase of the short-range probability density by more than two orders of magnitude, we predict significant gain in the photoassociation rates into deeply bound levels of the excited state by a second pulse, red-detuned relative to the first one, and conveniently delayed.

Study on Chemical Behavior of Energetic Deuterium Implanted into Li2TiO3

Deuterium ion implantation and subsequent X-ray Photoelectron Spectroscopy (XPS) and Thermal Desorption Spectroscopy (TDS) experiments were performed with varying implantation temperatures to reveal chemical behavior of tritium produced in Li2TiO3. These experimental results showed that there were four deuterium trapping states; two of which were interacted with and without oxygen near the surface, and the other two were interacted with E’-center and with oxygen with the formation of O-D bond in the bulk. These trapping states of deuterium in the bulk were almost the same as those of tritium generated in thermal neutron-irradiated Li2TiO3. The total amount of deuterium retention in the bulk was almost constant until O-D bonds formed in the bulk were decomposed, indicating that tritium trapping could proceed under hot atom chemical reactions. It was concluded that E’-center could trap the implanted deuterium more frequently than oxygen with the formation of O-D bonds in the bulk. Annihilations of them due to oxygen recovery could increase the retention of D with the formation of O-D bonds, resulting in the almost constant deuterium retention ratio up to its decomposition temperature of 573 K.

Detrapping behavior of tritium trapped via hot atom chemical process in neutron-irradiated ternary lithium oxides

Tritium detrapping behavior in neutron-irradiated ternary lithium oxides was investigated by the comparison of the annihilation of irradiation defects with the tritium release. It was revealed that the annihilation of irradiation defects would consist of two processes; namely the fast and the slow ones. The slow annihilation process has correlation with the tritium release, indicating that E′-center or F +-center could act as tritium trapping site, and from its activation energy of each sample, the annihilation of E′-center and F +-center could be attributed to the recovery of oxygen via diffusion, triggering the tritium release. Meyer–Neldel plots of these results indicate that the slow annihilation process was governed by the formation entropy of a pair of vacancy and interstitial atom of oxygen. Therefore, the trapped tritium would be detrapped by oxygen recovery to E′-center or F +-center, and its kinetics would be determined by the population of oxygen vacancy under thermal equilibrium.

Rebuttal to “Comment on the papers “Production of hot nitrogen atoms in the martian thermosphere” by F. Bakalian (2006), and “Monte Carlo computations of the escape of atomic nitrogen from Mars” by F. Bakalian and R.E. Hartle (2006)"

This response is to address some of the comments made by Dr. Fox and also to clarify some points in the Bakalian [2006. Icarus 183, 69–73] and Bakalian and Hartle [2006. Icarus 183, 55–68] papers. It is regrettable that some of the statements in the Bakalian and Bakalian and Hartle papers were misinterpreted.

Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space

A three‐dimensional (3‐D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O2+between 120 and 300 km and the sputtering of the Martian atmosphere by incident O+pickup ions. The reimpacting and escaping fluxes of pickup ions are derived from a 3‐D hybrid model describing the interaction of the solar wind with our computed Martian oxygen exosphere. In this work it is shown that the role of the sputtering crucially depends on an accurate description of the Martian corona as well as of its interaction with the solar wind. The sputtering contribution to the total oxygen escape is smaller by one order of magnitude than the contribution due to the dissociative recombination. The neutral escape is dominant at both solar activities (1 × 1025s−1for low solar activity and 4 × 1025s−1for high solar activity), and the ion escape flux is estimated to be equal to 2 × 1023s−1at low solar activity and to 3.4 × 1024s−1at high solar activity. This work illustrates one more time the strong dependency of these loss rates on solar conditions. It underlines the difficulty of extrapolating the present measured loss rates to the past solar conditions without a better theoretical and observational knowledge of this dependency.

Water bath calorimetry on a catalytic reaction of atomic hydrogen

Plasmas of certain catalysts such as Sr + and Ar + mixed with hydrogen were studied for evidence of a novel energetic reaction. These hydrogen plasmas called resonant transfer- or rt-plasmas were observed to form at low temperatures (e.g. ≈ 10 3 K ) and extraordinary low field strengths of about 1–2 V/cm when argon and strontium were present with atomic hydrogen. Time-dependent line broadening of the H Balmer α line was observed corresponding to extraordinarily fast H (25 eV). When an argon–hydrogen hollow-anode glow discharge plasma with strontium metal contained in the cell was optimized for Sr + emission, an average hydrogen hot atom temperature of 50.2 eV with a 83.5% population and an excess power of 28.5% of the input power were observed. Using water bath calorimetry, an excess power of 2.85 W was measured on rt-plasmas with Sr + and Ar + as catalysts and atomic hydrogen as a reactant, compared with controls with no hydrogen and no catalyst present. The energy balance was high. Given an argon–hydrogen (95/5%) flow rate of 1.0 sccm and an average excess power of 2.85 W, energy balances of over - 7.7 × 10 4 kJ/mol H 2 were measured.