Levels Of Atomic Hydrogen Research Articles

Collision Strengths and Effective Collision Strengths for Allowed Transitions among the n ≤ 5 Degenerate Levels of Atomic Hydrogen

We report calculations of collision strengths and effective collision strengths for 26 allowed transitions among the n≤ 5 degenerate levels of atomic hydrogen for which the close-coupling (CC) and Born approximations have been used. Results are listed over a wide range of energies (up to 100 Ryd) and temperatures (up to 107 K), sufficient for applications over a variety of plasmas, including fusion. Similar results have also been calculated for deuterium, but they negligibly differ with those of hydrogen.

Stability of Nonstationary Cooling of Pure Hydrogen Gas with Respect to the Number of Discrete Levels Taken into Account

The effect of the number K of atomic hydrogen levels taken into account on the cooling of the gas behind a shock front is studied. The calculations are done for the conditions in the atmospheres of long-period Mira Ceti type variables. K ranges from 2 to 25. The electron temperature Te(t; K) and ionization state x(r,K) asymptotically approach limiting functions Te(t) and x(t) that are independent of K. After the maximum electron temperature is reached, a partial equilibrium phase sets in, during which the populations of the highly excited discrete levels with principal quantum numbers ≥ 8 obey the Saha equation for the instantaneous electron temperature and density.

Experimental study of the electric field in a hollow cathode discharge in hydrogen: influence of sputtering

Doppler-free two photon optogalvanic spectroscopy was employed in extensive studies to measure the electric field strength in the cathode fall region of a hollow cathode discharge (HCD), operated in pure hydrogen, via the Stark splitting of the 2S level of atomic hydrogen. The high quality measurements, based on an improved cathode design and laser spectroscopic set-up, reveal clear differences in the recorded spectra obtained for different cathode material (stainless steel and tungsten) at otherwise identical discharge conditions. It is well known, that the sputtering rate of tungsten is about four orders of magnitude less compared to stainless steel; hence the hydrogen plasma in front of the stainless steel cathode is much more contaminated by iron compared to tungsten. This study is focussed on analyzing the distortion of the spectra, i.e. the corresponding local electric field strength, depending on cathode material and laser power. We refer the more pronounced distortion of the spectra in case of a stainless steel cathode to the related large contamination of the hydrogen plasma due to atomic iron which is also expanding into the central discharge. Spectra recorded for different laser power, i.e. different spectral irradiance, allow verifying spectroscopic conditions, where the distortion of the spectra becomes quite negligible even for stainless steel cathode.

Measured cathode fall characteristics depending on the diameter of a hydrogen hollow cathode discharge

In this work, Doppler-free two photon optogalvanic spectroscopy is used to measure the electric field strength in the cathode fall region of a hollow cathode discharge, operated in pure hydrogen, via the Stark splitting of the 2S level of atomic hydrogen. The cathode fall characteristics are analysed for various pressures and in a wide range of discharge currents. Tungsten is used as the cathode material, because it allows for reliable measurements in a fairly wide range of discharge conditions and because of its minimal sputtering. Two cathode diameters (10 mm and 15 mm) are used to study the dependence of the cathode fall on discharge geometry. The measurements reveal that the cathode fall characteristics are quite independent on the cathode diameter for equal cathode current density; hence the measurements can be used to test one dimensional modelling of the cathode fall region for low pressure hydrogen discharges using e.g. plane parallel electrodes.

Shielded hydrogen passivation – a novel method for introducing hydrogen into silicon

This paper reports a new approach for exposing materials, including solar cell structures, to atomic hydrogen. This method is dubbed Shielded Hydrogen Passivation (SHP) and has a number of unique features offering high levels of atomic hydrogen at low temperature whilst inducing no damage. SHP uses a thin metallic layer, in this work palladium, between a hydrogen generating plasma and the sample, which shields the silicon sample from damaging UV and energetic ions while releasing low energy, neutral, atomic hydrogen onto the sample. In this paper, the importance of the preparation of the metallic shield, either to remove a native oxide or to contaminate intentionally the surface, are shown to be potential methods for increasing the amount of atomic hydrogen released. Excellent, damage free, surface passivation of thin oxides is observed by combining SHP and corona discharge, obtaining minority carrier lifetimes of 2.2 ms and J0 values below 5.47 fA/cm2. This opens up a number of exciting opportunities for the passivation of advanced cell architectures such as passivated contacts and heterojunctions.

Optogalvanic spectroscopy applied to the study of hollow cathode discharges devices

Doppler free two-photon optogalvanic spectroscopy has been applied to measure the electric field strength in the cathode fall region of a hollow cathode discharge, via the Stark splitting of the 2S level of atomic hydrogen. Important improvements in the experimental arrangement and in our understanding of the discharge, have allowed us to measure accurately the dependence of the electric field with different parameters like the cathode material (stainless steel and tungsten), geometry (10 and 15 mm inner diameter) and the buffer gas. The study is done for different pressures and currents. The first results seem to reveal different behaviour in the electric field, depending on the material and geometry of the cathode and the discharge conditions.

Self-energy shift of the energy levels of atomic hydrogen in photonic crystal medium

Corrections to the average kinetic energy of atomic electrons caused by the change in electron mass in the photonic crystal medium are investigated. Corresponding shift of energy levels of atoms placed in a photonic crystal is shown to be of order of the ordinary Lamb shift.

Massive stars formed in atomic hydrogen reservoirs: H I observations of gamma-ray burst host galaxies

Long gamma-ray bursts (GRBs), among the most energetic events in the Universe, are explosions of massive and short-lived stars, so they pinpoint locations of recent star formation. However, several GRB host galaxies have recently been found to be deficient in molecular gas (H2), believed to be the fuel of star formation. Moreover, optical spectroscopy of GRB afterglows implies that the molecular phase constitutes only a small fraction of the gas along the GRB line-of-sight. Here we report the first ever 21 cm line observations of GRB host galaxies, using the Australia Telescope Compact Array, implying high levels of atomic hydrogen (HI), which suggests that the connection between atomic gas and star formation is stronger than previously thought, with star formation being potentially directly fuelled by atomic gas (or with very efficient HI-to-H2 conversion and rapid exhaustion of molecular gas), as has been theoretically shown to be possible. This can happen in low metallicity gas near the onset of star formation, because cooling of gas (necessary for star formation) is faster than the HI-to-H2 conversion. Indeed, large atomic gas reservoirs, together with low molecular gas masses, stellar and dust masses are consistent with GRB hosts being preferentially galaxies which have very recently started a star formation episode after accreting metal-poor gas from the intergalactic medium. This provides a natural route for forming GRBs in low-metallicity environments. The gas inflow scenario is also consistent with the existence of the companion HI object with no optical counterpart ~19 kpc from the GRB 060505 host, and with the fact that the HI centroids of the GRB 980425 and 060505 hosts do not coincide with optical centres of these galaxies, but are located close to the GRB positions.

Atomic population kinetics in fluctuating plasmas

A kinetic model for atomic populations in a turbulent plasma is developed in the framework of the so-called continuous time random walk theory. A special emphasis is devoted to the role of temperature fluctuations. With an application to the 1s, 2s and 2p levels of atomic hydrogen, we demonstrate that a resonance effect can be observed.

STUDIES OF Λ(1405) WITH K-MESIC ATOMS

Experimental tests of the Λ(1405) properties are suggested. These could reflect the position and shape of this state in the [Formula: see text] channel. The first test consists in precise determinations of the level widths in the highest accessible K -mesic atom states. One needs to study the dependence of these widths on the binding energy of the valence protons in the involved nuclei. The second test consists in the measurement of radiative transitions from the P-wave atomic hydrogen levels to the Λ(1405) state. In both cases one can study the absorptive part of [Formula: see text] scattering amplitude in the subthreshold region.

From cold to fusion plasmas: spectroscopy, molecular dynamics and kinetic considerations

Non-equilibrium effects in hydrogen plasmas have been investigated in different systems, ranging from RF plasmas to corona discharges. The existing measurements of vibrational and rotational temperatures, obtained by different spectroscopical techniques, are reported, rationalized by results calculated by kinetic models. Input data of these models are discussed with particular attention on the dependence of relevant cross sections on the vibrational quantum number. Moreover, the influence of the vibrational excitation of H2 molecules on the translational distribution of atoms in ground and excited levels is shown. Finally, a collisional radiative model for atomic hydrogen levels, based on the coupling of the Boltzmann equation for electron energy distribution function (EEDF) and the excited state kinetics, is presented, emphasizing the limits of quasi-stationary approximation. In the last case, large deviations of the EEDF and atomic level distributions from the equilibrium are observed.

Hollow cathode fall field strength measured by Doppler-free two-photon optogalvanic spectroscopy via Stark splitting of the 2S level of hydrogen

It has recently been demonstrated that Doppler-free two-photon optogalvanic spectroscopy is very well suited to measure the strong electric field strength (0.4 kV/cm to 4 kV/cm) present in the cathode fall of hollow cathode discharges, via the Stark splitting of the 2S level of atomic hydrogen and its isotopes. Based on an improved reliability and precision of the measurements, the aim of the present study is to analyze more deeply the dependence of the cathode fall behaviour for a hydrogen discharge on the usual discharge parameters like gas pressure and discharge current; and for changes of the discharge geometry using two different cathode diameters of 10 mm and 15 mm.

Energy levels of atomic hydrogen in a closed box: A natural cutoff criterion of the electronic partition function

The radial part of the Schrodinger equation for atomic hydrogen in a spherical box of radius is numerically solved. Two sets of energy levels are obtained, the first one reproduces the unperturbed bound levels up to a given principal quantum number while the other one unbound describes levels with energy greater than the unperturbed ionization energy of atomic hydrogen EH. These last levels asymptotically converge to the corresponding set which can be obtained by the particle in the box model, i.e., levels which increase their energy as n2 thus ensuring the convergence of the electronic partition function.

Requirements for cosmological 21-cm masers

We perform Monte-Carlo calculations of the radiative transfer of Lyα photons emitted by a source embedded in a neutral collapsing gas cloud. This represents a young galaxy or quasar during the early stages of the epoch of reionisation (EoR). After computing the Lyα spectrum as function of radius and time, we find that the Lyα color temperature may be negative in large volumes surrounding the central source. Motivated by this result, we explore the prospects for a population inversion in the hyperfine levels of atomic hydrogen via the Wouthuysen–Field (WF) effect. The reason for this exploration is clear: if 21-cm masers exist during the EoR, they could greatly boost the expected 21-cm flux from this epoch. We find that population inversion is unlikely to occur for several reasons: (1) the required Lyα luminosities of the central source exceed ∼1045ergs−1. The radiation pressure exerted by such a large Lyα flux likely halts the collapse of the cloud; (2) when quantum corrections to the WF-coupling strength are applied, the required Lyα luminosities are (even) larger by orders of magnitude; (3) a relatively low flux of Lyα photons that is produced via other channels (X-ray heating, collisional excitation of hydrogen) prevents the Lyα color temperature from becoming negative.

Calculation of low-lying levels of atomic hydrogen in a magnetic field with a finite basis set from B-splines

A finite-basis-set method has been developed to calculate energy levels of low-lying states of atomic hydrogen in a magnetic field. The wavefunctions are expanded in terms of a B-spline basis in the radial direction and spherical harmonics in the angular direction. Energy levels are presented for the states 1s0, 2p0 and 2p−1 with a magnetic field strength range from zero up to 2.35 × 107 T. The obtained results are compared with available data and found to be in much better agreement with high accuracy energies reported in the literature than those from other approaches. The accuracy of energies for the excited state 2p0 exceeds that of previous high accuracy calculations when B> 10 au.

Doppler-free Stark spectroscopy of the second excited level of atomic hydrogen for measurements of electric fields

The Stark splitting of the second excited level of atomic hydrogen (with principal quantum number $n=3$) has been measured by pulsed laser spectroscopy in order to determine small electric fields by optical means. Doppler-free excitation with two counterpropagating laser beams at $205\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ allows us to measure the $n=3$ Stark spectra either by an optogalvanic signal after ionization by a third laser photon or by detection of the Balmer-$\ensuremath{\alpha}$ fluorescence photons emitted by the excited atoms. Three different cases of laser polarization have been investigated in order to evaluate the possibilities and limitations of this one-step laser excitation method for electric field determination, especially at field strengths below $200\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{cm}$. The method provides the best field sensitivity achieved with lower excited levels that can be reached directly by two-photon absorption from the ground state (in contrast to the more sensitive Rydberg levels). For this purpose, an advanced tunable pulsed uv laser with narrow bandwidth almost at the Fourier limit has been used. The high spectral resolution allowed us to deduce electric field strengths as small as $50\phantom{\rule{0.3em}{0ex}}\mathrm{V}∕\mathrm{cm}$ from the frequency shift between two selected isolated Stark components. As a main advantage, this simple analysis of the measured spectra does not rely on knowledge of the line intensities which may be strongly affected by the measuring conditions.

Energy levels of atomic hydrogen in germanium from ab-initio calculations

Donor and acceptor levels of atomic hydrogen centers in germanium are calculated by density functional-pseudopotential modeling, using large hydrogen-terminated Ge clusters. We found that the neutral bond centered (BC) and anti-bonding configurations (AB) are energetically very close, with a slight (0.1 eV) preference for the BC structure, which agrees with recent muonium spin resonance (μSR) data and previous supercell ab-initio calculations. The interstitial H defect shows a negative-U level ordering, possessing donor and acceptor levels at 0.28 eV below the conduction band and at about 0.1–0.2 eV above the valence band, respectively. The calculated donor level accounts well for deep level transient spectroscopy (DLTS) and μSR data, which give a (0/+) transition at 0.11 and 0.23 eV below E c, respectively. The acceptor transition involves a structural change between AB and BC forms. Considering the 0.1 eV difference between these configurations, the AB 0→AB –+h + vertical transition is placed below E v+0.1 eV, which may explain the failure of DLTS in detecting such a shallow level.

Use of fluorescence spectroscopy of hydrogen atoms and BH molecules for measurements of electric fields in a plasma

Two laser-aided techniques for electric field (EF) measurements in a plasma have been realized. The first technique is based on the use of Stark splitting of high-lying levels of atomic hydrogen, whereas the second technique is based on the use of Stark mixing of the Λ-doublet energy sublevels of boron monohydride molecules. Both diagnostic techniques have been applied to the measurements of EFs in a hollow cathode discharge. The results of the EF measurements obtained by both techniques are in good agreement. The strength of the EF in a hollow cathode discharge was in the range of 1000–2600 V cm−1 for the dark space region and in the range of 200–300 V cm−1 for the negative glow region.

New power source from fractional quantum energy levels of atomic hydrogen that surpasses internal combustion

Extreme ultraviolet (EUV) spectroscopy was recorded on microwave discharges of helium with 2% hydrogen. Novel emission lines were observed with energies of q·13.6 eV where q=1,2,3,4,6,7,8,9, or 11 or these lines inelastically scattered by helium atoms wherein 21.2 eV was absorbed in the excitation of He (1s 2) to He (1s 12p 1). These lines were identified as hydrogen transitions to electronic energy levels below the ‘ground’ state corresponding to fractional quantum numbers. Significant line broadening corresponding to an average hydrogen atom temperature of 33–38 eV was observed for helium–hydrogen discharge plasmas; whereas pure hydrogen showed no excessive broadening corresponding to an average hydrogen atom temperature of ≈3 eV. Since a significant increase in H temperature was observed with helium–hydrogen discharge plasmas, and energetic hydrino lines were observed at short wavelengths in the corresponding microwave plasmas that required a very significant reaction rate due to low photon detection efficiency in this region, the power balance was measured on the helium–hydrogen microwave plasmas. With a microwave input power of 30 W, the thermal output power was measured to be at least 300 W corresponding to a reactor temperature rise from room temperature to 900 °C within 90 s, a power density of 30 MW/m 3, and an energy balance of about −4×10 5 kJ/mol H 2 compared to the enthalpy of combustion of hydrogen of −241.8 kJ/mol H 2.

Differential cross sections and cross-section ratios for the electron-impact excitation of the neon2p53sconfiguration

Electron-impact differential cross-section measurements for the excitation of the ${2p}^{5}3s$ configuration of Ne are reported. The Ne cross sections are obtained using experimental differential cross sections for the electron-impact excitation of the $n=2$ levels of atomic hydrogen [Khakoo et al., Phys. Rev. A 61, 012701-1 (1999)], and existing experimental helium differential cross-section measurements, as calibration standards. These calibration measurements were made using the method of gas mixtures (Ne and H followed by Ne and He), in which the gas beam profiles of the mixed gases are found to be the same within our experimental errors. We also present results from calculations of these differential cross sections using the R-matrix and unitarized first-order many-body theory, the distorted-wave Born approximation, and relativistic distorted-wave methods. Comparison with available experimental differential cross sections and differential cross-section ratios is also presented.