Metastable Hydrogen Research Articles

Laser-assisted relativistic ionization of the metastable atomic hydrogen H(2S) by electron impact in the coplanar binary geometry

Laser-assisted relativistic ionization of the metastable atomic hydrogen H(2S) by electron impact in the coplanar binary geometry

Double Differential Cross-sections for Ionization of Metastable 2P-state Hydrogen Atoms by Electrons at Intermediate Energies with Exchange Effects

Double differential cross sections were obtained from the triple differential cross sections. The present calculations are compared with the hydrogenic ground-state experimental data, theoretical results, and DDCS first Born results. Discrepancies have been found between the present results and those measurements and theoretical results and also qualitative agreement with those of compared theories. The exchange effect results give an enormous prospect for experimental outcomes in the field of ionization problems. We are expecting that the present study makes more significant contribution to the study of atomic scattering problems using the multiple scattering theories. In the future calculations, other kinematic conditions or other atomic species will also be interesting and significant.

Influence of high energy electrons on negative ion density in a hot cathode discharge

This study investigates the influence of high energy electrons on the negative ion density along with the effect of filament current, discharge voltage, pressure, and magnetic filter field strength by carrying out measurements of negative ion density in a hot cathode discharge system in the double plasma device using a Langmuir probe technique. In the volume production technique, negative ions are formed by the dissociative attachment of low energy electrons to metastable hydrogen molecules and among the negative ion loss mechanisms; the presence of high energy electrons in the plasma is one of the important factors. Although the magnetic filter could reduce the temperature of the electrons in the target region considerably, high energy electrons were still present in the diffusion region, which could reduce the negative ion density. Negative hydrogen ion density measured by using Langmuir probe in the target region is also compared with the particle balance model considering the set of reactions involved in the production and destruction of negative ions, and a reasonably good match between them has been observed.

Direct observation of transitions between quantum states with energy differences below 10 neV employing a Sona unit

The direct access to atomic transitions between close by quantum states employing standard spectroscopic methods is often limited by the size of the necessary radio-frequency cavities. Here we report on a new tool for fundamental spectroscopy measurements that can overcome this shortcoming. For this, a Sona transition unit was used, i.e., two opposed solenoidal coils that provide an oscillating field in the rest frame of the through-going atomic beam. In this way, we were able to control the induced photon energy down to 10 neV or f sim MHz. The tuneable parameter is the velocity of the atomic beam. For illustration of the method, we report a measurement of the hyperfine splitting energies between the substates with F=1 and m_F = -1, 0, +1 of 2S_{1/2} metastable hydrogen atoms as function of a magnetic field.Graphic

The Hydrates of TEMPO: Water Vibrations Reveal Radical Microsolvation.

An organic radical monohydrate complex is detected in vacuum isolation at low temperature by FTIR supersonic jet spectroscopy for the first time. It is shown to exhibit a rich conformational and vibrational coupling dynamics, which can be drastically reduced by appropriate isotope substitution. Its detection with a new gas recycling infrared spectrometer demonstrates the thermal metastability of the gaseous TEMPO radical even under humid gas conditions. Compared to its almost isoelectronic and isostructural, closed shell ketone analogue, the hydrogen bond of the solvating water is found to be less directional, but stronger and more strongly downshifting the bonded water OH stretch vibration. A second solvent water directs the first one into a metastable hydrogen bond position to solvate the nitrogen center and the first water at the same time.

The Hydrates of TEMPO: Water Vibrations Reveal Radical Microsolvation

AbstractAn organic radical monohydrate complex is detected in vacuum isolation at low temperature by FTIR supersonic jet spectroscopy for the first time. It is shown to exhibit a rich conformational and vibrational coupling dynamics, which can be drastically reduced by appropriate isotope substitution. Its detection with a new gas recycling infrared spectrometer demonstrates the thermal metastability of the gaseous TEMPO radical even under humid gas conditions. Compared to its almost isoelectronic and isostructural, closed shell ketone analogue, the hydrogen bond of the solvating water is found to be less directional, but stronger and more strongly downshifting the bonded water OH stretch vibration. A second solvent water directs the first one into a metastable hydrogen bond position to solvate the nitrogen center and the first water at the same time.

On the stability of the metastable phase of atomic hydrogen

The possibility of metastable hydrogen formation was studied in details using the density functional theory. It was shown that the I41/amd structure of atomic metallic hydrogen could be dynamically stable in the pressure range of 175-500 GPa. The results of calculations of structural, energy characteristics and phonon spectra of the normal phase are presented.

Two-level systems and growth-induced metastability in hydrogenated amorphous silicon

Specific heat measurements from 2 to 300 K of hydrogenated amorphous silicon prepared by hot-wire chemical vapor deposition show a large excess specific heat at low temperature, significantly larger than the Debye specific heat calculated from the measured sound velocity. The as-prepared films have a Schottky anomaly that is associated with metastable hydrogen in the amorphous network, as well as large linear and excess cubic term commonly associated with tunneling two-level systems in amorphous solids. Annealing at 200 °C, a temperature that enables hydrogen mobility but not evaporation, irreversibly reduces the heat capacity, eliminating the Schottky anomaly and leaving a reduced linear heat capacity. A non-monotonic dependence on growth temperature and H content is observed in all effects, except for sound velocity, which suggests that the tunneling two-level systems and the Schottky anomaly are associated with atomic hydrogen and require low density regions to form, while sound velocity is associated with the silicon network and increases with increasing growth temperature.

Experimental and Theoretical Study of Electronic and Hyperfine Properties of Hydrogenated Anatase (TiO2): Defect Interplay and Thermal Stability

In this study we report on the results from emission $^{57}$Fe M${\"o}$ssbauer Spectroscopy experiments, using dilute $^{57}$Mn implantation into pristine (TiO$_2$) and hydrogenated anatase held at temperatures between 300-700 K. Results of the electronic structure and local environment are complemented with ab-initio calculations. Upon implantation both Fe$^{2+}$ and Fe$^{3+}$ are observed in pristine anatase, where the latter demonstrates the spin-lattice relaxation. The spectra obtained for hydrogenated anatase show no Fe$^{3+}$ contribution, suggesting that hydrogen acts as a donor. Due to the low threshold, hydrogen diffuses out of the lattice. Thus showing a dynamic behavior on the time scale of the $^{57}$Fe 14.4 keV state. The surrounding oxygen vacancies favor the high-spin Fe$^{2+}$ state. The sample treated at room temperature shows two distinct processes of hydrogen motion. The motion commences with the interstitial hydrogen, followed by switching to the covalently bound state. Hydrogen out-diffusion is hindered by bulk defects, which could cause both processes to overlap. Supplementary UV-Vis and electrical conductivity measurements show an improved electrical conductivity and higher optical absorption after the hydrogenation. X-ray photoelectron spectroscopy at room temperature reveals that the sample hydrogenated at 573 K shows presence of both Ti$^{3+}$ and Ti$^{2+}$ states. This could imply that a significant amount of oxygen vacancies and -OH bonds are present in the samples. Theory suggests that in the anatase sample implanted with Mn(Fe), probes were located near equatorial vacancies as next-nearest-neighbours, whilst a metastable hydrogen configuration is responsible for the annealing behavior.

Cryogenic atomic hydrogen beam apparatus with velocity characterization.

Precision spectroscopy of hydrogen often relies on effusive thermal atomic beams, and the uncertainty in the velocity distribution of these beams can introduce systematic errors and complicate lineshape models. Here, we present an apparatus capable of high signal-to-noise studies of these velocity distributions at cryogenic temperatures for both ground state (1S) and metastable (2S) hydrogen using a simple time-of-flight technique. We also investigate how the cryogenic nozzle geometry affects these results.

Metastable Conducting Crystalline Hydrogen at High Pressure

The quantum molecular dynamics method within the density functional theory has been used to calculate the equation of state, pair correlation function, and static electrical conductivity of solid hydrogen in the region of formation of a conducting phase. Hysteresis has been revealed on the density dependence of the pressure at a temperature of 100 K under compression and subsequent tension. The overlapping of branches of the isotherms of the molecular and nonmolecular phases of solid hydrogen corresponds to the region of existence of metastable states. The width of this region is 275 GPa. It has been shown that conducting crystalline nonmolecular hydrogen with P21/c symmetry can exist at extension to a pressure of 350 GPa.

Metastable molecular fluid hydrogen at high pressures

Warm dense hydrogen is studied in the region of fluid–fluid phase transition within the framework of the density functional theory. We report a procedure of obtaining metastable states and calculate the equation of state. Metastable states are diagnosed by pair correlation functions and values of conductivity. We obtain a strong overlapping through the density of metastable and equilibrium branches of pressure isotherms. This indicates the plasma nature of the phase transition.

Pressure shifts in high-precision hydrogen spectroscopy. I. long-range atom–atom and atom–molecule interactions

We study the theoretical foundations for the pressure shifts in high-precision atomic beam spectrosopy of hydrogen, with a particular emphasis on transitions involving higher excited P states. In particular, the long-range interaction of an excited hydrogen atom in a 4P state with a ground-state and metastable hydrogen atom is studied, with a full resolution of the hyperfine structure. It is found that the full inclusion of the 4P_1/2 and 4P_3/2 manifolds becomes necessary in order to obtain reliable theoretical predictions, because the 1S ground state hyperfine frequency is commensurate with the 4P fine-structure splitting. An even more complex problem is encountered in the case of the 4P-2S interaction, where the inclusion of quasi-degenerate 4S-2P_1/2 state becomes necessary in view of the dipole couplings induced by the van der Waals Hamiltonian. Matrices of dimension up to 40 have to be treated despite all efforts to reduce the problem to irreducible submanifolds within the quasi-degenerate basis. We focus on the phenomenologically important second-order van der Waals shifts, proportional to 1/R^6 where R is the interatomic distance, and obtain results with full resolution of the hyperfine structure. The magnitude of van der Waals coefficients for hydrogen atom-atom collisions involving excited P states is drastically enhanced due to energetic quasi-degeneracy; we find no such enhancement for atom-molecule collisions involving atomic nP states, even if the complex molecular spectrum involving ro-vibrational levels requires a deeper analysis.

Pressure shifts in high-precision hydrogen spectroscopy. I. Long-range atom–atom and atom–molecule interactions

We study the theoretical foundations for the pressure shifts in high-precision atomic beam spectrosopy of hydrogen, with a particular emphasis on transitions involving higher excited P states. In particular, the long-range interaction of an excited hydrogen atom in a 4P state with a ground-state and metastable hydrogen atom is studied, with a full resolution of the hyperfine structure. It is found that the full inclusion of the 4P1/2 and 4P3/2 manifolds becomes necessary in order to obtain reliable theoretical predictions, because the 1S ground state hyperfine frequency is commensurate with the 4P fine-structure splitting. An even more complex problem is encountered in the case of the 4P–2S interaction, where the inclusion of quasi-degenerate 4S–2P1/2 state becomes necessary in view of the dipole couplings induced by the van der Waals Hamiltonian. Matrices of dimension up to 40 have to be treated despite all efforts to reduce the problem to irreducible submanifolds within the quasi-degenerate basis. We focus on the phenomenologically important second-order van der Waals shifts, proportional to 1/R6 where R is the interatomic distance, and obtain results with full resolution of the hyperfine structure. The magnitude of van der Waals coefficients for hydrogen atom–atom collisions involving excited P states is drastically enhanced due to energetic quasi-degeneracy; we find no such enhancement for atom–molecule collisions involving atomic nP states, even if the complex molecular spectrum involving ro-vibrational levels requires a deeper analysis.

Dense quantum hydrogen

Ultracondensed fluid metallic hydrogen has been made at high pressures. Solid metallic H would have several scientific and technological applications if metallic fluid hydrogen made at high pressures could be quenched metastably to a solid at ambient. The quantum nature of dense hydrogen is an issue both at high pressures and in materials recovered metastably on release of pressure. Quantum zero point vibrations of H might have a significant affect on properties of metallic H at high pressures and might adversely affect lifetimes of metastable solid hydrogen, which is particularly relevant for applications. Metallic (degenerate) fluid H has been made at finite temperatures with a reverberating shock wave under dynamic compressions and under static compressions in laser-heated diamond-anvil cells. The pressure-temperature (P–T) regime in those experiments ranged up to 180 GPa and 3000 K, in which metallic fluid H is a quantum-degenerate fluid with T/TF << 1, where TF is Fermi temperature. The lifetime of an experiment under static compression near 500 GPa at 5.5 K ranged up to weeks, sufficiently long to warrant concern about quantum diffusion having a major affect on the chemical composition of that metallic sample.

Towards a first measurement of the free neutron bound beta decay detecting hydrogen atoms at a throughgoing beamtube in a high flux reactor

In addition to the common 3-body decay of the neutron n → pe-ν̅e there should exist an effective 2-body subset with the electron and proton forming a Hydrogen bound state with well defined total momentum, total spin and magnetic quantum numbers. The atomic spectroscopic analysis of this bound system can reveal details about the underlying weak interaction as it mirrors the helicity distributions of all outgoing particles. Thus, it is unique in the information it carries, and an experiment unravelling this information is an analogue to the Goldhaber experiment performed more than 60 years ago. The proposed experiment will search for monoenergetic metastable BoB H atoms with 326 eV kinetic energy, which are generated at the center of a throughgoing beamtube of a high-flux reactor (e.g., at the PIK reactor, Gatchina). Although full spectroscopic information is needed to possibly reveal new physics our first aim is to prove the occurrence of this decay and learn about backgrounds. Key to the detection is the identification of a monoerergtic line of hydrogen atoms occurring at a rate of about 1 s−1 in the environment of many hydrogen atoms, however having a thermal distribution of about room temperature. Two scenarios for velocity (energy) filtering are discussed in this paper. The first builds on an purely electric chopper system, in which metastable hydrogen atoms are quenched to their ground state and thus remain mostly undetectable. This chopper system employs fast switchable Bradbury Nielsen gates. The second method exploits a strongly energy dependent charge exchange process of metastable hydrogen picking up an electron while traversing an argon filled gas cell, turning it into manipulable charged hydrogen. The final detection of hydrogen occurs through multichannel plate (MCP) detector. The paper describes the various methods and gives an outlook on rates and feasibility at the PIK reactor in Gatchina.

Ionization of Hydrogenic 3d State by Electron Impact

The triple differential cross sections estimation have been ascertained theoretically for the ionization of metastable 3d-state hydrogen atoms by electron at 150 eV, 200 eV and 250 eV for assorted kinematic conditions exerting a multiplex scattering principle. The existent new-findings are assimilated with the theoretic data of hydrogenic metastable 2S, 3S and 3P states as well as the hydrogenic ground state experiment. An analysis of the attained observations reveals qualitative fitness with those of compared results specially with hydrogenic ground state BBK model, ground state experimental data and metastable state 2S state results. This is a new theoretical work on hydrogenic metastable 3d state ionization by electron. The substantial progress of the current study offers a wide scope for empirical study in ionization process.

Ionisation of metastable 3P-state hydrogen atom by electron with exchange effects

In the present work, the triple-differential cross-sections (TDCSs) for the ionisation of metastable 3P-state hydrogen atoms at an incident electron energy of 250 eV with exchange effects are computed in the asymmetric coplanar geometry for various kinematic conditions. The final-state wave function of Das and Seal (Phys. Rev. A 47, 2978 (1993)) is used here. The results of the present calculation are compared with the available hydrogenic ground-state experimental data and other existing theoretical results. An analysis of the results reveals qualitative enhancement with other compared results. The implication of the present study offers an extensive scope for experimental verification in such a field of ionisation.

Comprehensive asymmetric dark matter model

Asymmetric dark matter (ADM) is motivated by the similar cosmological mass densities measured for ordinary and dark matter. We present a comprehensive theory for ADM that addresses the mass density similarity, going beyond the usual ADM explanations of similar number densities. It features an explicit matter-antimatter asymmetry generation mechanism, has one fully worked out thermal history and suggestions for other possibilities, and meets all phenomenological, cosmological and astrophysical constraints. Importantly, it incorporates a deep reason for why the dark matter mass scale is related to the proton mass, a key consideration in ADM models. Our starting point is the idea of mirror matter, which offers an explanation for dark matter by duplicating the standard model with a dark sector related by a $Z_2$ parity symmetry. However, the dark sector need not manifest as a symmetric copy of the standard model in the present day. By utilising the mechanism of "asymmetric symmetry breaking" with two Higgs doublets in each sector, we develop a model of ADM where the mirror symmetry is spontaneously broken, leading to an electroweak scale in the dark sector that is significantly larger than that of the visible sector. The weak sensitivity of the ordinary and dark QCD confinement scales to their respective electroweak scales leads to the necessary connection between the dark matter and proton masses. The dark matter is composed of either dark neutrons or a mixture of dark neutrons and metastable dark hydrogen atoms. Lepton asymmetries are generated by the $CP$-violating decays of heavy Majorana neutrinos in both sectors. These are then converted by sphaleron processes to produce the observed ratio of visible to dark matter in the universe. The dynamics responsible for the kinetic decoupling of the two sectors emerges as an important issue that we only partially solve.

Controlled hydrogen release from metastable hydrides

Metastable hydrides are an interesting class of hydrogen carrier since many offer high volumetric and gravimetric hydrogen densities and rapid hydrogen release rates at low temperatures. Unlike reversible metal hydrides, which operate near equilibrium, metastable hydrogen carriers rely on kinetic barriers to limit or prevent the release of hydrogen and can be prepared in a stabilized state far from equilibrium. Despite the advantage of low temperature hydrogen release, this type of one-way thermolysis reaction can be difficult to control since the hydrogen release rate varies with temperature and composition. Here we developed a kinetic rate equation from a series of isothermal measurements, which describes the relationship between temperature, hydrogen release rate and composition for aluminum hydride. This equation is necessary to thermally control the rate of hydrogen release throughout decomposition. This equation was used to run a fuel cell at a controlled rate of ∼1 wt%/hr. Although the equation established in this paper relates specifically to aluminum hydride, the method used is applicable to other metastable hydrides.