Ground-state Hydrogen Research Articles

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.

Two photon absorption laser induced fluorescence measurements of neutral density in a helicon plasma

We have developed a new diagnostic based on two-photon absorption laser induced fluorescence (TALIF). We use a high intensity (5 MW/cm2), narrow bandwidth (0.1 cm−1) laser to probe the ground state of neutral hydrogen, deuterium and krypton with spatial resolution better than 0.2 cm, a time resolution of 10 ns, and a measurement cadence of 20 Hz. Here, we describe proof-of-principle measurements in a helicon plasma source that demonstrate the TALIF diagnostic is capable of measuring neutral densities spanning four orders of magnitude; comparable to the edge neutral gradients predicted in the DIII-D tokamak pedestal. The measurements are performed in hydrogen and deuterium plasmas and absolute calibration is accomplished through TALIF measurements in neutral krypton. The optical configuration employed is confocal, i.e., both light injection and collection are accomplished with a single lens through a single optical port in the vacuum vessel. The wavelength resolution of the diagnostic is sufficient to separate hydrogen and deuterium spectra and we present measurements from mixed hydrogen and deuterium plasmas that demonstrate isotopic abundance measurements are feasible. Time resolved measurements also allow us to explore the evolution of the neutral hydrogen density and temperature and effects of wall recycling. We find that the atomic neutral density grows rapidly at the initiation of the discharge, reaching the steady-state value within 1 ms. Additionally, we find that neutral hydrogen atoms are born with 0.08 eV temperatures, not 2 eV as is typically assumed.

A subquantum arrow of time

The outcome of a single quantum experiment is unpredictable, except in a pure-state limit. The definite process that takes place in the apparatus may either be intrinsically random or be explainable from a deeper theory. While the first scenario is the standard lore, the latter implies that quantum mechanics is emergent. In that case, it is likely that one has to reconsider radiation by accelerated charges as a physical effect, which thus must be compensated by an energy input. Stochastic electrodynamics, for example, asserts that the vacuum energy arises from classical fluctuations with energy 1/2ℏω per mode. In such theories the stability of the hydrogen ground state will arise from energy input from fluctuations and output by radiation, hence due to an energy throughput. That flux of energy constitutes an arrow of time, which we call the "subquantum arrow of time". It is related to the stability of matter and it is more fundamental than, e.g., the thermodynamic and cosmological arrows.

Development of a Lyman-α laser system for spectroscopy and laser cooling of antihydrogen

Hydrogen Lyman-α radiation (121.56 nm) is important because it allows for the excitation and detection of ground-state hydrogen atoms by a one-photon process. The trapping of antihydrogen, recently reported by the ALPHA collaboration at CERN, has revived interest in Lyman-α lasers. In order to perform high precision tests of matter-antimatter symmetry violations or gravity-antimatter interactions with antihydrogen, laser cooling using the 1s − 2p single photon transition is essential. Recent theoretical simulations predict that even with a pulsed Lyman-α source, laser cooling of antihydrogen would be possible. Here we describe the implementation of a high power vacuum-ultraviolet (VUV) laser at the Lyman-α transition of hydrogen. The VUV light was generated using a two-photon-resonant four-wave mixing process in a phase-matched mixture of krypton and argon. Two wavelengths (ωR → 202.31 and ωT → 602.56 nm) were mixed in a sum-difference scheme (ωVUV = 2ωR − ωT) with a two-photon resonance at (4s24p55p[1/2]0 ← 4s24p6(1S0)) transition in Kr. With an Ar/Kr mixture of 3.9:1 we obtained 10 ns pulses of 0.1 μJ of energy at a repetition rate of 10 Hz.

Atomic photoionization and dynamical stabilization with subrelativistically intense high-frequency light: Magnetic-field effects revisited

The results of three-dimensional numerical simulations of strong-field atomic stabilization with arbitrarily polarized light beyond the electric dipole approximation are presented. The study of the long-term evolution of the ground-state hydrogen atom exposed to an intense high-frequency laser field reveals the persistence of the metastable bound states up to relativistic intensities. The population of these states in a pulsed field is examined as a function of the pulse peak intensity. These calculations resolve recent contradictions in the literature related to the role of magnetic field in the high-frequency stabilization phenomenon.

Exploring high-energy doubly excited states of NH by dissociative recombination of NH+

We have investigated electron capture by NH+ resulting in dissociative recombination (DR). The impact energies studied of ∼4–12 eV extend over the range below the two lowest predicted NH+ dissociative states in the Franck–Condon (FC) region of the ion. Our focus has been on the final state populations of the resulting N and H atoms. The neutral DR fragments are detected downstream of a merged electron and ion beam interaction zone in the TSR storage ring, which is located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Transverse fragment distances were measured on a recently developed high count-rate imaging detector. The distance distributions enabled a detailed tracking of the final state populations as a function of the electron collision energy. These can be correlated with doubly excited neutral states in the FC region of the ion. At low electron energy of ∼5 eV, the atomic product final levels are nitrogen Rydberg states together with ground-state hydrogen. In a small electron energy interval near 7 eV, a significant part of the final state population forms hydrogen Rydberg atoms with nitrogen atoms in the first excited () term, showing the effect of Rydberg doubly excited states below the predicted 2 2Π ionic potential. The distance distributions above ∼10 eV are compatible with nitrogen Rydberg states correlating to the doubly excited Rydberg state manifold below the ionic 2 4Σ− level.

Precision measurement of the (3p–1s) X-ray transition in muonic hydrogen

The (3p — 1s) X-ray transition to the muonic hydrogen ground state was measured with a highresolution crystal spectrometer. The assumption of a statistical population of the hyperfine levels of the muonic hydrogen ground state was directly confirmed by the experiment and measured values for the hyperfine splitting can be reported. The measurement supplements studies on line broadening effects induced by Coulomb de-excitation hindering the direct extraction of the pion-nucleon scattering lengths from pionic hydrogen and deuterium X-ray lines.

Imaging of spatial many-body wave functions via linear momentum measurements

The equivalence of a complete characterization of linear momenta of fragments from a many-body fragmentation process and the spatial wave function of the many-body system is discussed. Our experiment on three-body dissociation of state selected H3 and D3 molecules into ground-state hydrogen atoms strongly suggests the existence of such a close relationship as it is also predicted by theory in the form of the imaging theorem. We conclude that prudent imaging of many-body fragmentation provides a laboratory view of the squared many-body wave function at a spatial scale of molecular dimensions at which fragments exit into the realm of independent free particles.

Non linear optical analyses of hexamine: Phenol cocrystals based on hydrogen bonding: A comparative study

Fourier-Transform Infrared (FT-IR) spectroscopy supported by Raman spectroscopy has been employed to explain the conventional and unconventional hydrogen bonding present in the 4,4′thiodiphenol: hexamine and 4,4′sulfonyldiphenol: hexamine cocrystals. The possible internal and external vibrational modes are predicted through factor group analysis. Influence of intra molecular charge transfer (ICT) interaction caused by the strong ionic ground state hydrogen bonding between charged species, giving rise to a non centro symmetric structure which is a criterion for second harmonic generation (SHG) efficiency has been discussed. Intense low wave number hydrogen bond vibrations in Raman which arise due to electron–phonon coupling are analyzed. Optical quality of adducts is identified through UV–Vis analysis. The second harmonic generation efficiency of both adducts is determined by Kurtz–Perry method.

Attractive Optical Forces from Blackbody Radiation

Blackbody radiation around hot objects induces ac Stark shifts of the energy levels of nearby atoms and molecules. These shifts are roughly proportional to the fourth power of the temperature and induce a force decaying with the third power of the distance from the object. We explicitly calculate the resulting attractive blackbody optical dipole force for ground state hydrogen atoms. Surprisingly, this force can surpass the repulsive radiation pressure and actually pull the atoms against the radiation energy flow towards the surface with a force stronger than gravity. We exemplify the dominance of the "blackbody force" over gravity for hydrogen in a cloud of hot dust particles. This overlooked force appears relevant in various astrophysical scenarios, in particular, since analogous results hold for a wide class of other broadband radiation sources.

Precision experiments and fundamental physics at low energies – Part I

Precision experiments and fundamental physics at low energies – Part I

Scattering properties of ground-state spin-polarized atomic hydrogen

In this paper, the scattering properties of ground-state spin-polarized atomic hydrogen (H↓) are studied at 0K using the Lippmann–Schwinger formalism. The total, diffusion and viscosity cross sections, as well as the S-wave scattering length, are calculated. The S-wave scattering cross section is found to be the most significant partial wave contributing to the total cross section at low energy. The contribution of the higher angular momentum waves, especially the D-wave (ℓ=2), to the scattering increases with increasing relative momentum k. Our calculations are performed for three triplet-state potentials: Morse-type, Silvera and Born–Oppenheimer potentials. It is also noted that as k→0, the results of the Morse potential are larger than those of the Silvera and Born–Oppenheimer potentials. This is because of the exponential tail of the Morse potential which falls off more rapidly than the r−6 behavior of the Silvera and Born–Oppenheimer potentials. Also, the Morse potential is relatively shallower than the other two potentials. For high k, the Morse cross sections approach the corresponding Silvera cross sections. This is because these triplet-state potentials have almost the same short-range part. The total cross sections reflect the quantum oscillations arising from the diffraction caused by the repulsive short-range part of the potential. Our results are consistent with those obtained by other methods.

Calculations of neutral fractions and angular distributions for H(1s) and H+ impinging on Al(111) at grazing incidence

We have computed H(1s) angular distributions and the corresponding neutral fractions for ground state hydrogen atoms and protons impinging on an Al(111) surface under a grazing angle of incidence of 0.56° within the 1–100keV impact energy range. Capture and loss for resonant and Auger processes are taken into account as well as the surface-plasmon-assisted electron capture mechanism. Comparisons between our calculations and available experimental angular distributions at 25keV allow to some extent to discriminate between the various theoretical reports used in the present work for the resonant process transition rates. The same kind of comparison for a lower impact energy like 6.25keV, for which we report predictive results, would allow to better identify the correct result (if any) for the resonant mode and in that way to gain insight on the theoretical description of the very near surface region.

Proton Transfer Assisted Charge Transfer Phenomena in Photochromic Schiff Bases and Effect of –NEt2 Groups to the Anil Schiff Bases

Photochromic Schiff bases 5-diethylamino-2-[(4-diethylamino-benzylidene)-hydrazonomethyl]-phenol (DDBHP) and N,N'-bis(4-N,N-diethylaminosalisalidene) hydrazine (DEASH) with both the proton and charge transfer moieties have been synthesized, and their photophysical properties such as excited state intramolecular charge transfer (ICT) and proton transfer (ESIPT) processes have been reported on the basis of steady-state and time-resolved spectral measurement in various solvents. The ground-state six-membered intramolecular hydrogen bonding network at the proton transfer site accelerates the ESIPT process for these compounds. Both the compounds show large Stokes-shifted emission bands for proton transfer and charge transfer processes. The hydrogen bonding solvents play a crucial role in these photophysical processes. Excited-state dipole moment of DDBHP and DEASH calculated by the solvatochromic method supports the polar character of the charge transfer excited state. Introduction of -NEt(2) groups to the reported salicylaldehyde azine (SAA) Schiff base results an increase in fluorescence lifetime from femtosecond to picosecond time scale for the proton transfer process.

Two-photon ionization of ground state hydrogen from the photoelectric threshold up to 40 keV

Our study of the ionization of the 1s state of the hydrogen atom through the absorption of two identical photons covers a region of higher energies than those considered up to now; it aims to establish the region of validity of nonrelativistic dipole approximation for the total generalized cross section.

Quantum characteristics of the hydrogen bond

Most analyses of hydrogen bond strengths and dynamics (e.g. vibrational spectroscopy and transport) have been considered in terms of (model) potential energy functions defined at the Born–Oppenheimer level of approximation. This paper reports an analysis of the quantum dynamics of hydrogen in the bond that focuses on the quantum ground state of the binding hydrogen in the fields of the other atoms. In view of its mass and size, hydrogen is delocalized in its bond much as is the electron in a covalent bond. It is shown, under certain circumstances, that the compression of the A–B distance, with hydrogen in the A–H–B bond space, yields a flatter effective A–B bond potential due to the reduction of hydrogen density along the direct AB bond line. The quantum behaviour of bonding hydrogen also influences dynamical processes such as vibrational spectroscopy and hydrogen or proton transport. †Also Adjunct Professor, Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 3J5 Canada.

Unusually kicked dynamics: Hydrogen atom in a spherical box

Abstract In this paper we have examined the ionization of the ground state hydrogen atom in a spherical box with laser pulses of specific shapes. These shapes are predicted assuming correspondence under some conditions with the alternating kicking field. Unusually kicked dynamics is suggested. It is shown that such kicked dynamics leads to generalized Rabi oscillations with the positive energy states included and participation of the excited states. The correspondence with the real pulse is established emphasizing such unusually kicked dynamics. The approach is verified on the one-dimensional (1D) hydrogen atom and calculation of the known results for ionization probability.

Electron capture cross section in collision of multi-charged neon ions with ground state hydrogen and helium

The classical trajectory Monte Carlo method and the post form of three-body boundary corrected continuum intermediate state (BCCIS-3B) approximation are employed to calculate the cross sections for total and state-selective electron capture in collision of highly charged Neq+ ions with ground state hydrogen atom in the intermediate to high energy region. In both these methods, the active electron interactions with the partially stripped neon ions are described by a model potential containing both a long-range part and a short-range part. We have also calculated the double electron-capture cross sections in collision of fully stripped neon ion with helium atom in the energy range 80–2,000 keV/amu using the post-form of four-body BCCIS approximation (BCCIS-4B). In BCCIS formalism, the intermediate continuum state of the active electrons with the projectile ion has been taken into account as the projectile charge is greater than the target charge. In addition, state-selective charge transfer cross sections are given in tabular and graphical form.

ChemInform Abstract: Intermetallic Hydrides: A Review with Ab Initio Aspects

AbstractReview: 113 refs.

Convergence of the multipole expansions of the polarization and dispersion interactions for atoms under confinement

The multipole expansion of the polarization interaction between a charged particle and an electrically neutral object has long been known to be asymptotic in nature, i.e., the multiple expansion diverges at any finite distance from the atom. However, the multipole expansion of the polarization potential of a confined hydrogen atom is shown to be absolutely convergent at a distance outside the confinement radius, R(0), of the atom. The multipole expansion of the dispersion potential between two confined hydrogen atoms is also shown to be absolutely convergent provided the two atoms satisfy R > 2R(0), where R is the inter-nuclear separation. These results were established analytically using oscillator strength sum rules and verified numerically using a B-spline description of the hydrogen ground state and its excitation spectrum.