Ground-state Hydrogen Research Articles

Triple differential cross-sections for the ionization of metastable 2P-state hydrogen atoms by electrons with exchange effects

In this paper, triple differential cross-sections for the ionization of metastable 2P-state hydrogen atoms by 250 eV electron energy with exchange effects for various kinematic conditions are calculated. Multiple scattering theory proposed by Das and Seal in Phys. Rev. A 47, 2978 (1993) is utilized here. The computational results provide significant peak features that show good qualitative agreement with the hydrogenic ground-state experimental data and theoretical results and the present first Born results. In addition, physical origin of the peaks of the cross-section curves is investigated.

Pressure effect on hydrogen tunneling and vibrational spectrum inα-Mn

The pressure effect on the tunneling mode and vibrational spectra of hydrogen in $\ensuremath{\alpha}\ensuremath{-}{\text{MnH}}_{0.07}$ has been studied by inelastic neutron scattering. Applying hydrostatic pressure of up to 30 kbar is shown to shift both the hydrogen optical modes and the tunneling peak to higher energies. First-principles calculations show that the potential for hydrogen in $\ensuremath{\alpha}$-Mn becomes overall steeper with increasing pressure. At the same time, the barrier height and its extent in the direction of tunneling decrease and the calculations predict significant changes of the dynamics of hydrogen in $\ensuremath{\alpha}$-Mn at 100 kbar, when the estimated tunneling splitting of the hydrogen ground state exceeds the barrier height.

Steps towards the hyperfine splitting measurement of the muonic hydrogen ground state: pulsed muon beam and detection system characterization

The high precision measurement of the hyperfine splitting of the muonic-hydrogen atom ground state with pulsed and intense muon beam requires careful technological choices both in the construction of a gas target and of the detectors. In June 2014, the pressurized gas target of the FAMU experiment was exposed to the low energy pulsed muon beam at the RIKEN RAL muon facility. The objectives of the test were the characterization of the target, the hodoscope and the X-ray detectors. The apparatus consisted of a beam hodoscope and X-rays detectors made with high purity Germanium and Lanthanum Bromide crystals. In this paper the experimental setup is described and the results of the detector characterization are presented.

On the Stability of Classical Orbits of the Hydrogen Ground State in Stochastic Electrodynamics

De la Peña 1980 and Puthoff 1987 show that circular orbits in the hydrogen problem of Stochastic Electrodynamics connect to a stable situation, where the electron neither collapses onto the nucleus nor gets expelled from the atom. Although the Cole-Zou 2003 simulations support the stability, our recent numerics always lead to self-ionisation. Here the de la Peña-Puthoff argument is extended to elliptic orbits. For very eccentric orbits with energy close to zero and angular momentum below some not-small value, there is on the average a net gain in energy for each revolution, which explains the self-ionisation. Next, an 1 / r 2 potential is added, which could stem from a dipolar deformation of the nuclear charge by the electron at its moving position. This shape retains the analytical solvability. When it is enough repulsive, the ground state of this modified hydrogen problem is predicted to be stable. The same conclusions hold for positronium.

Calculations of Triple Differential Cross-Sections for the Ionization of H (3S) by Electron Impact

In the present study we have calculated the Triple Differential Cross-Sections (TDCS) for the ionization of metastable 3S-state hydrogen atoms at 250 eV incidence electron energy for various kinematic conditions in the asymmetric coplanar geometry. A final state wave function of multiple scattering theory [11] has been used in the present study. The present results show a good qualitative agreement with the existing hydrogenic ground state experimental data and various related theoretical results. Some results of hydrogenic metastable states are also presented here for comparisons. However there is no existing theoretical and experimental works on hydrogenic metastable 3S-state except an existing theoretical first born result of Vuc<img width="7" height="16" src="http://article.sciencepublishinggroup.com/journal/122/1221089/image001.png" />i<img width="7" height="16" src="http://article.sciencepublishinggroup.com/journal/122/1221089/image001.png" /> et al. [19].

Velocity-selected magnetic guiding of Zeeman-decelerated hydrogen atoms

An original design of magnetic guide is presented, suitable for use with Zeeman-decelerated supersonic beams of ground-state hydrogen atoms and other light paramagnetic species. Three-dimensional particle trajectory simulations show that, by combining a series of permanent-magnet Halbach arrays with pulsed high-current wire electromagnets, this guide can be used to efficiently transmit the slow, decelerated atoms and discard the faster, undecelerated atoms and other species in the gas beam. The curved guide would be suitable for guiding hydrogen atoms into an ion trap to investigate low temperature ion-molecule collisions. It is also shown that the device could be used for the guiding or velocity selection from an undecelerated supersonic or effusive beam.

Simulation of the hydrogen ground state in stochastic electrodynamics

Stochastic electrodynamics is a classical theory which assumes that the physical vacuum consists of classical stochastic fields with average energy in each mode, i.e., the zero-point Planck spectrum. While this classical theory explains many quantum phenomena related to harmonic oscillator problems, hard results on nonlinear systems are still lacking. In this work the hydrogen ground state is studied by numerically solving the Abraham–Lorentz equation in the dipole approximation. First the stochastic Gaussian field is represented by a sum over Gaussian frequency components, next the dynamics is solved numerically using OpenCL. The approach improves on work by Cole and Zou 2003 by treating the full problem and reaching longer simulation times. The results are compared with a conjecture for the ground state phase space density. Though short time results suggest a trend towards confirmation, in all attempted modellings the atom ionises at longer times.

Modeling the Histidine-Phenylalanine Interaction: The NH···π Hydrogen Bond of Imidazole·Benzene.

NH···π hydrogen bonds occur frequently between the amino acid side groups in proteins and peptides. Data-mining studies of protein crystals find that ∼80% of the T-shaped histidine···aromatic contacts are CH···π, and only ∼20% are NH···π interactions. We investigated the infrared (IR) and ultraviolet (UV) spectra of the supersonic-jet-cooled imidazole·benzene (Im·Bz) complex as a model for the NH···π interaction between histidine and phenylalanine. Ground- and excited-state dispersion-corrected density functional calculations and correlated methods (SCS-MP2 and SCS-CC2) predict that Im·Bz has a Cs-symmetric T-shaped minimum-energy structure with an NH···π hydrogen bond to the Bz ring; the NH bond is tilted 12° away from the Bz C6 axis. IR depletion spectra support the T-shaped geometry: The NH stretch vibrational fundamental is red shifted by -73 cm(-1) relative to that of bare imidazole at 3518 cm(-1), indicating a moderately strong NH···π interaction. While the S0(A1g) → S1(B2u) origin of benzene at 38 086 cm(–1) is forbidden in the gas phase, Im·Bz exhibits a moderately intense S0 → S1 origin, which appears via the D(6h) → Cs symmetry lowering of Bz by its interaction with imidazole. The NH···π ground-state hydrogen bond is strong, De=22.7 kJ/mol (1899 cm–1). The combination of gas-phase UV and IR spectra confirms the theoretical predictions that the optimum Im·Bz geometry is T shaped and NH···π hydrogen bonded. We find no experimental evidence for a CH···π hydrogen-bonded ground-state isomer of Im·Bz. The optimum NH···π geometry of the Im·Bz complex is very different from the majority of the histidine·aromatic contact geometries found in protein database analyses, implying that the CH···π contacts observed in these searches do not arise from favorable binding interactions but merely from protein side-chain folding and crystal-packing constraints. The UV and IR spectra of the imidazole·(benzene)2 cluster are observed via fragmentation into the Im·Bz+ mass channel. The spectra of Im·Bz and Im·Bz2 are cleanly separable by IR hole burning. The UV spectrum of Im·Bz2 exhibits two 000 bands corresponding to the S0 → S1 excitations of the two inequivalent benzenes, which are symmetrically shifted by -86/+88 cm(-1) relative to the 000 band of benzene

Simulation of the Hydrogen Ground State in Stochastic Electrodynamics-2: Inclusion of Relativistic Corrections

In a recent paper the authors studied numerically the hydrogen ground state in stochastic electrodynamics (SED) within the the non-relativistic approximation. In quantum theory the leading non-relativistic corrections to the ground state energy dominate the Lamb shift related to the photon cloud that should cause the quantum-like behaviour of SED. The present work takes these corrections into account in the numerical modelling. It is found that they have little effect; the self-ionisation that occurs without them remains present. It is speculated that the point-charge approximation for the electron is the cause of the failure.

A Global Enhanced Vibrational Kinetic Model for High-Pressure Hydrogen RF Discharges

A global enhanced vibrational kinetic model (GEVKM) is developed for multitemperature, chemically reacting hydrogen plasmas in inductively coupled cylindrical discharges for lowto high-pressure regimes. The species in a GEVKM are ground-state hydrogen atoms H and molecules H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , 14 vibrationally excited hydrogen molecules H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (v), v = 1 - 14, electronically excited hydrogen atoms H(2) and H(3), groundstate positive ions H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> , ground-state negative ions H <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> , and electrons e. The GEVKM involves volume-averaged steady-state continuity equations for the plasma species, an electron energy equation, a total energy equation, a heat transfer equation to the chamber walls, and a comprehensive set of surface and volumetric chemical processes governing vibrational and ionization kinetics of hydrogen plasmas. The GEVKM is verified and validated by comparisons with previous numerical simulations and experimental measurements of a negative hydrogen ion source in the low-pressure (20-100 mtorr), low-absorbed-power-density (0.053-0.32 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) regime and of a microwave plasma reactor in the intermediate to high-pressure (1-100 torr), high-absorbed-power-density (8.26-22 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) regime. The GEVKM is applied to the simulation of a high-current negative hydrogen ion source (HCNHIS). The HCNHIS consists of a high-pressure (20-65 torr) radio-frequency discharge chamber in which the main production of high-lying vibrational states of the hydrogen molecules occurs, a bypass system, and a low-pressure (0.1-0.4 torr) negative hydrogen ion production region where negative ions are generated by the dissociative attachment of low-energy electrons to rovibrationally excited hydrogen molecules. The discharge pressure and negative hydrogen ion current predicted by the GEVKM compare well with the measurements in the HCNHIS.

Ionization characteristics of the hydrogen ground state in an intense high-frequency laser field

Ionization characteristics of the hydrogen ground state in an intense high-frequency laser field

Toward the measurement of the hyperfine splitting in the ground state of muonic hydrogen

The recent Lamb shift experiment at PSI and the controversy about proton size revived the interest in measuring the hyperfine splitting in muonic hydrogen and extracting the proton Zemach radius. The efficiency of the experimental method depends on the energy dependence of the muon transfer rate to higher-Z gases in the near epithermal energy range. As long as the available experimental data only give the average transfer rate in the whole epithermal range, and the detailed theoretical calculations have not yet been verified, an experiment has been started for the measurement of the transfer rate in thermalized gas target at different temperatures and extracting from the data an estimate of the transfer rate for arbitrary energies. We outline the underlying mathematical method and estimate its accuracy.

Compton profile of molecular hydrogen**Project supported by the National Natural Science Foundation of China (Grant Nos. U1332204, 11274291, and 11104309), the National Basic Research Program of China (Grant No. 2010CB923301), and the Fundamental Research Funds for the Central Universities, China. The experiment was carried out in a beam time approved by Shanghai Synchrotron Radiation Facility (SSRF), China (Proposal Nos. 11sr0210,

The Compton profile of molecular hydrogen has been determined at an incident photon energy of 20 keV based on the third generation synchrotron radiation, and the statistical accuracy of 0.2% is achieved at pz = 0. Different theoretical methods, i.e., the density functional method, and the Hartree–Fock method, were used to calculate the Compton profiles of hydrogen with different basis sets, and the theoretical calculations are in agreement with the experimental observation in the whole pz region. Compared with the HF calculation, the DFT-B3LYP ones are in better agreement with the present experiment, which indicates the electron correlation effect is very important to describe the wavefunction in the ground state of hydrogen.

Time–Energy Uncertainty and Electronic Correlation in H+–Graphite Collisions

The formation of negative ions in the scattering of protons by a highly oriented pyrolytic graphite (HOPG) surface is theoretically and experimentally analyzed for a large scattering angle and compared with previous results obtained in the same system but for a forward scattering geometry. These experiments were motivated by the fact that the interaction of a hydrogen atom with a surface is the prototype system for studying the intra-atomic Coulomb repulsion in an s-like valence orbital localized in the atom. We tried to answer the open questions related to the electronic correlation effects and the influence of the detailed surface band structure by using appropriate theoretical models. The comparison with the experiment of theoretical results obtained by using different limit approximations of the electronic repulsion in the atomic state shows the expected validity ranges according to the ion velocity. However, the most remarkable conclusion obtained from this comparison is the nonvalidity of an adiabatic picture of the energy levels shifted by the interactions with the surface atoms, when the energy uncertainty introduced by the ion velocity becomes of the order of the electronic repulsion in the hydrogen ground state.

Energy Spectrum of Ejected Electrons of H(2P) Ionization by Electrons in Coplanar Asymmetric Geometry

We have investigated the energy spectrum of ejected electrons of hydrogen atoms ionization from metastable 2P state by electrons in coplanar asymmetric geometry. A multiple scattering theory of Das and Seal is applied. The present results show very interesting binary peak features. As well as a significant qualitative agreement with hydrogenic ground state results is obtained. New theoretical results and experimental verification for such treatment in hydrogenic metastable states by electrons will be interesting.

Intense laser field and conduction band-edge nonparabolicity effects on hydrogenic impurity states of InGaN QW

In this paper, hydrogenic impurity ground-state binding energy in unstrained wurtzite (In, Ga)N symmetric quantum well is investigated. The heterostructure is considered under the action of an intense laser field (ILF) incorporating an additional internal probe as well as the conduction band-edge nonparabolicity effect (CBENP). The variational approach is used within the framework of single band effective-mass approximation with two-parametric 1S-hydrogenic trial wavefunction. The competition effect between internal and external perturbations is also shown. Our results reveal that the binding energy is the largest for the well width around the effective Bohr radius and is strongly influenced by both parameters. Moreover, the principle effect of ILF (CBENP) is to reduce (enhance) the binding energy. It is found that the lift of the conduction band-edge can be easily eliminated by adjusting the ILF-parameter.

Field-ionization threshold and its induced ionization-window phenomenon for Rydberg atoms in a short single-cycle pulse

We study the field-ionization threshold behavior when a Rydberg atom is ionized by a short single-cycle pulse field. Both hydrogen and sodium atoms are considered. The required threshold field amplitude is found to scale inversely with the binding energy when the pulse duration becomes shorter than the classical Rydberg period, and, thus, more weakly bound electrons require larger fields for ionization. This threshold scaling behavior is confirmed by both three-dimensional classical trajectory Monte Carlo simulations and numerically solving the time-dependent Schr\"odinger equation. More surprisingly, the same scaling behavior in the short pulse limit is also followed by the ionization thresholds for much lower bound states, including the hydrogen ground state. An empirical formula is obtained from a simple model, and the dominant ionization mechanism is identified as a nonzero spatial displacement of the electron. This displacement ionization should be another important mechanism beyond the tunneling ionization and the multiphoton ionization. In addition, an ``ionization window'' is shown to exist for the ionization of Rydberg states, which may have potential applications to selectively modify and control the Rydberg-state population of atoms and molecules.

Ground and excited state hydrogen bonding effects of 6-aminocoumarin in water: An ab initio study

The hydrogen bonded complexes of 6-aminocoumarin (6AC) with several water molecules in their ground and lowest excited singlet electronic state have been investigated using the ab initio methods. It was shown that the complex containing five water molecules in the surrounding of the amino group of the 6AC molecule has the lowest stabilization energy in the ground electronic state. This complex can serve as a model of the first solvation shell of the 6AC molecule in bulk water. The energies of hydrogen bonds formed by the carbonyl group with up to two water molecules were also determined. The calculated change in the total hydrogen bond energy due to S0→S1 excitation is in good agreement with the experimental data [E. Krystkowiak, A. Maciejewski, Phys. Chem. Chem. Phys. 2011;13:11317–11324]. The maxima of absorption spectra of the hydrogen-bonded complexes, calculated taking into account nonspecific solute–solvent interactions, are in reasonable agreement with the experimental data.

Twisted intramolecular charge transfer and its contribution to the NLO activity of Diglycine Picrate: A vibrational spectroscopic study

Single crystals of Diglycine Picrate (DGLP) were grown by slow evaporation technique and the vibrational spectral analysis is carried out using FT Raman and FT-IR spectroscopy, supported by Density Functional Theoretical (DFT) computations to derive equilibrium geometry, vibrational wavenumbers and first hyperpolarizability. The vibrational spectra confirm the existence of NH3+ in DGLP. The influence of Twisted Intramolecular Charge Transfer (TICT) caused by the strong ionic ground state hydrogen bonding between charged species making DGLP crystal to have the non-centrosymmetric structure has been discussed. The Natural Bond Orbital (NBO) analysis confirms the occurrence of strong intermolecular NH⋯O hydrogen bond. The HOMO–LUMO energy gap and the first order hyperpolarizability were calculated and it supports the nonlinear optical activity of the Diglycine Picrate crystal.

Impact Excitations of Hydrogen Atoms in Collisions with Protons and Antiprotons

The direct impact excitations of ground-state hydrogen atoms by protons and antiprotons are investigated by using an impact parameter treatment. The calculations are performed within the solution of the coupled differential equations arising from the one-center atomic-orbital close-coupling approach as well as the impact parameter version of the first and second Born approximations. We have considered calculations that allow couplings to the n=1−5 states (up to g sub-levels) of the target atom as well as others, which neglect the effect of all states other than the initial and final states of the target atom. The sensitivity of the cross sections to the charge of the projectile is studied. The calculated cross sections are compared with those obtained by previous theoretical and experimental results.