Excited Hydrogen Atoms Research Articles

The photoionization of excited hydrogen atom in plasmas

The photoionization processes of excited hydrogen atoms in plasma environments are investigated using the method of complex coordinate rotation. The standard Debye–Hückel model and modified Debye–Hückel model are adopted to describe the plasma screening effects. The photoionization cross sections of plasma-embedded excited hydrogen atoms varied with different screening lengths are displayed to illustrate the influence of plasma screening. The results of the Debye–Hückel model compared with the modified Debye–Hückel are presented. The shape resonances and Cooper minima due to the plasma screening are observed and discussed.

Low-frequency strong-field ionization and excitation of hydrogen atom

The dynamics of hydrogen atom in the presence of a strong radiation field of the titanium-sapphire laser is studied for the Keldysh parameters γ ≥ 1 and γ ≤ 1. It is demonstrated that the ionization is supplemented with the effective population of the excited states with the principal quantum numbers n = 5–10 in the entire range of variation in the Keldysh parameter. The population of the excited Rydberg states can be interpreted as a consequence of the multiphoton resonance involving the initial 1s state and a group of excited states in the vicinity of the continuum boundary with the simultaneous repopulation of these states by Λ-type Raman transitions under the action of the laser field. The resulting coherent Rydberg packet appears to be stable with respect to ionization, so that the ionization of the atomic system in the presence of strong electromagnetic field is suppressed. Physical reasons for the stabilization are discussed. An interpretation of the effective population of the Rydberg states in the recent experiments on the ionization of atomic helium by the titanium-sapphire laser is proposed.

Linear Polarization of Photons Emitted from Excited Hydrogen Atoms Formed above Metal Surfaces

AbstractThis paper presents theoretical results for linear polarization of Lyman‐α and Balmer‐α emission following single electron capture by hydrogen nuclei to excited levels above Mo surfaces. The polarization degrees are evaluated for photons from the hydrogen atoms outgoing along surface normal with translation velocities of 0.05‐1 au. In this geometry, the excited states are aligned with respect to the surface normal (quantization axis). Finite polarization degrees are obtained for electric‐dipole photons emitted at right angle to the surface normal; the linear polarization preferentially along the surface plane at lower translation velocities turns to the surface normal at higher velocities (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Small phase-space structures and their relevance to pulsed quantum evolution: Stepwise ionization of the excited hydrogen atom in a microwave pulse

Experiments have shown that the microwave ionization probability of a highly excited almost monodimensional hydrogen atom subjected to a microwave pulse sometimes grows in steps when the peak electric field of the pulse is increased. Classical pulsed simulations display the same steps, which have been traced to phase-space metamorphoses. Quantum numerical calculations again exhibit the same ionization steps. I show that the time-sequence of two level interactions, responsible for the observed steps in the quantum picture, is strictly related to the classical phase space structures generated by the above mentioned metamorphoses.

Positron-Impact Excitation of Hydrogen Atoms in Debye Plasmas

The positron-impact excitation of hydrogen atoms embedded in plasma environments is investigated using the close-coupling approximation from the low to intermediate energy region without including any positronium formation channel, and the excitation cross sections for 1s → 2s, 1s → 2p and 2s → 2p processes are calculated in a wide Debye parameter range. The screening interactions, described by the Debye–Hückel model, decrease the coupling matrix elements, resulting in the reduction of the excitation cross sections from a few percent to one magnitude of ten. This will alter remarkably the spectroscopy of hydrogen in intensity and position, which should be considered in the simulation and diagnostics under some specific plasma conditions.

10.1007/s11443-008-2003-8

To explain the variety of observed optical emission stratification in the shells around Wolf-Rayet stars, we have calculated the nonstationary cooling of a homogeneous gas layer heated to a temperature (0.4–2) × 105 K. We have assumed that the nebula is ionized by its central star and consists of a rarefied gas and a set of clouds with different densities through which adiabatic shock waves produced by the stellar wind propagate. Based on this model, we have determined the sequence in which the emission in Hα and in nebular oxygen lines appears. The Hα emission attributable to the electron-collision excitation of hydrogen atoms is produced earliest on the periphery of nebulae, the [O III] line emission follows next, and, finally, the Hα recombination emission is produced. The results obtained are in good agreement with the observational data.

Hot hydrogen atoms in a water-vapor microwave plasma source

A study of the hydrogen Balmer line shape in a water-vapor, microwave slot-antenna excited plasma source operated at 2.45 GHz is reported. The emission profiles of the H α and H β lines are well fitted by Gaussian profiles. Excited hydrogen atoms are detected in the remote plasma zone of the source up to 30 cm distance from the exciting antennas. The measured Doppler temperature corresponding to the H β line broadening is about three times higher than the rotational temperature of the hydrogen molecular Fulcher-α band. It has been found clear evidence for the existence of a local source of excited “hot” hydrogen atoms in the “microwave field free” remote plasma zone. The measured Doppler broadening of the O(777.4 nm) triplet line indicates that “hot” oxygen atoms, with an energy around 0.3 eV, are also created in this source. Exothermic electron–ion and ion–ion recombination processes as well as DC distributed potentials existing in inhomogeneous remote plasma are possible local sources of “hot” atoms in the far remote plasma zone.

Collision Integrals for Interactions Involving Atoms in Electronically Excited States

Transport collision integrals for low-lying excited states of nitrogen atoms and ions are derived in the framework of a phenomenological approach following, where possible, also the traditional multipotential procedure. The two sets of results are compared considering critically the observed deviations, and finally, the proposed model is validated by comparison with oxygen atom-atom interactions. In addition, an attempt is made to extend the proposed phenomenological method to interactions involving high-lying excited states, taking into account the symmetric interaction of two excited hydrogen atoms, characterized by increasing principal quantum number.

Electron excitation of hydrogen atom by ions impact in the energy range 20–1000 keV/amu

We have calculated the electron excitation cross sections of hydrogen atom by the impact of protons, alpha particles and He+ ions using the boundary corrected continuum intermediate state approximation in the intermediate and high energies. The calculated results are compared with other theoretical and experimental results. The angular influence of excitation to the H atom at the intermediate energy is also discussed. The distortion effects due to the projectile charges in reactions of electron excitation to bound states of the target H atom are shown in the intermediate and high collision energy.

Optical radiation and ionization of hydrogen atoms in heterogeneous exothermal reactions proceeding in an electric field

Optical radiation related to the Balmer series (Hα, Hβ, Hγ) of hydrogen atoms is discovered when studying the isothermal reaction of trimeric acetone peroxide decomposition on the surface of oxidized tungsten in a static electric field with a strength of up to 4 × 106 V/cm at T = 300 K. The distance from the surface over which desorbing excited hydrogen atoms radiate is determined from the Stark splitting of the lines. Electronically excited atoms remaining on the surface ionize according to the surface ionization mechanism.

Excitation of hydrogen atoms at intermediate and high energies by proton impact under a three-body Born–Faddeev-type formalism

In this work, differential cross sections have been calculated for the excitation of atomic hydrogen (H) from its ground state (1s) into a selection of its excited states (2s, 2p0, 2p±1 and 3s). The present study was conducted at intermediate and high proton impact energies within the range 50 keV–1 MeV. A three-body model based on Faddeev-type equations is implemented, while near the energy shell the two-body Coulomb transition matrix was used to calculate the transition amplitude. Second and higher order approximations have been ignored in this case. The resulting amplitudes are subsequently utilized to calculate total and differential cross sections for the corresponding excitation processes. These calculated cross sections have then been compared with available experimental data and other theoretical results from the literature.

Signature of fast H atoms from cathode glow region of a dc discharge

Asymmetric broadening of Hα line from cathode glow region has been studied. In the cathode glow, mean energy and fractional population of very fast hydrogen atoms were found to be ∼130 eV and ∼55%, respectively. These values reduced to ∼90 eV and ∼20% when measured at negative glow region. The observed asymmetry was attributed to the presence of the fast hydrogen atoms near the cathode surface. The mean energy and number density of excited fast hydrogen atoms were estimated from the velocity distribution of H+, H2+, and H3+ considering collisions inside the cathode sheath. The reduction in the mean energy and number density of the excited fast hydrogen atoms, at the other locations of the discharge, was explained by energy relaxation and thermalization of the neutrals with the background gas.

Electron capture from excited hydrogen atoms by highly charged beryllium and carbon ions

The cross sections for electron capture in collisions of bare and helium-like ions of Be and C with excited H atoms (n = 2) have been calculated by a molecular-state close-coupling method in a collision energy range of 60 eV/amu-6 keV/amu. Calculated results show that these cross sections are remarkably larger than those for collisions with ground-state H atoms. For example, for collisions of Be2+, Be4+, C4+, and C6+ ions with H(2s) atoms at ∼1 keV/amu, the cross sections are 190 _ 10–16 cm2, 610 _ 10–16 cm2, 920 _ 10–16 cm2, and 720 _ 10–16 cm2, respectively. In contrast, the cross sections for collisions with ground-state H atoms are 25 _ 10–16 cm2, 35 _ 10–16 cm2, 30 _ 10–16 cm2, and 40 _ 10–16 cm2, respectively.

Collisional effects in the far red wing of Lyman-$\sf \alpha$

Context. An accurate determination of the line broadening of the Lyman series of atomic hydrogen has been shown to be fundamental to interpretating UV and FUV spectra of DA white dwarfs. Quasi-molecular lines have been detected in the red wing of Lyman-α, Lyman-β, and Lyman-γ. They arise from radiative collisions of excited atomic hydrogen with unexcited neutral hydrogen atoms or protons. Aims. The aim of this paper is twofold. First, we examine the range of validity of the one-perturber approximation widely used to calculate the line wing. Second, we study the relative contributions of the two main transitions contributing to the far wing of the Lyman-α line profile according to the effective temperature and perturber density. Methods. In cool white dwarfs, the perturber density is so high that the one-perturber approximation breaks down and the collisional effects must be treated by using the autocorrelation formalism in order to take into account simultaneous collisions with more than one perturbing atom. Results. We show that, at the low temperatures of cool white dwarfs, the contribution of the singlet X 1 Σ + → B 1 Σ + transition cannot be neglected in the calculation of Lyman-α profile perturbed by neutral hydrogen. A comparison with experimental laboratory spectra shows that the effects of multiple H-perturbers appear in the far wing. Conclusions. A reliable determination of the line profiles for the physical conditions of cool white dwarfs requires a unified theory that takes account of both the singlet and triplet transitions contributing to Lyman-α using accurate interaction potentials and radiative dipole transition moments. Multiple perturber effects must be considered and the autocorrelation formalism permits calculations for the densities of the atmospheres of cool white dwarfs.

Investigation of amplification process on the third Stokes line of H_2 under ultraviolet laser irradiation

An amplification process was investigated in the third stimulated Raman scattering (SRS) line of H2 excited with a 266 nm laser beam generated from the fourth harmonic of a Nd:YAG laser. The unexpected intensity enhancement observed at the third Stokes SRS line around 397.8 nm is attributed to the seeding of the self-generated H-epsilon Balmer line at 397 nm of atomic hydrogen by pumping the H2 molecule with a high-energy laser pulse at 266 nm. It is worth mentioning that in our case the SRS spectrum of H2 showed a quite different intensity pattern from the usual SRS spectra of hydrogen. The pulse energy and pressure dependence of all the SRS lines in general and the third Stokes SRS line in particular were investigated, and in all respects the amplified SRS line at 397.8 nm manifested completely different characteristics that have not been reported in previous publications. The conversion efficiency (CE) of all the SRS lines in the hydrogen 266 nm SRS spectrum was also estimated, and 36% CE was achieved at the 397.78 nm line. To support our claim for amplification at the third Stokes line by seeding of the H-epsilon Balmer line of atomic hydrogen, a comparative study was also carried out by pumping hydrogen gas with 355 nm (less energy per photon) and 266 nm laser beams. It is worth noting that amplification of the third Stokes SRS line was observed only with the 266 nm pump laser, where dissociation of H2 and excitation of atomic hydrogen take place, and not with the 355 nm pump laser.

Long-range interaction between ground and excited state hydrogen atoms

The asymptotic expansion at large distances is obtained for the interaction between a ground state hydrogen atom and an excited hydrogen atom with principal quantum number n = 2, …, 10. A degenerate perturbation theory up to the second order is employed to obtain accurate results. The asymptotic representation for several special cases is found in the limit of large quantum number n.

Application of the Second Born Approximation to Excitation of Hydrogen Atoms by Protons and Antiprotons Impact

We present and compare total cross sections for excitation in collisions of protons and antiprotons with hydrogen atoms in the 2s state. Calculations are performed in the framework of the second Born approximation, in the energy range of 5-1000keV. We apply the usual approach of the second Born approximation, which approximates the summation raised by retaining few terms, as well as another approach approximates all energies corresponding to the intermediate states to that corresponding to the initial state. The annihilation effect in the case of the antiproton collision is investigated. We compare the results with the previous theoretical calculations.

Luminescence from low-energy impact of [formula omitted] and [formula omitted] ions (n = 1,2,3) on a Tore Supra carbon tile

The hydrogen Balmer series was observed when beams of H+, H2+, H3+ and D+, D2+, D3+ ions impinged at 100–1000eV on a carbon fiber composite tile (Tore Supra). The excitation functions of the Hβ (Dβ) lines demonstrate the validity of the independent particle model. The logarithmic plot of the Hβ (Dβ) line intensity versus the reciprocal projectile ion velocity can be well reproduced by a model in which the hydrogen ion projectiles are neutralized in the entrance phase and subsequently electronically excited in collisions with carbon atoms. Finally, the excited hydrogen atoms leave the solid and emit the observed photons, unless they are quenched in non-radiative processes.

Dual site observations of dayside Doppler-shifted hydrogen profiles: preliminary results

Simultaneous optical ground-based observations of auroral Balmer excited hydrogen atoms were performed during the boreal winters of 2002–2003 and 2003–2004 at Ny-Ålesund, Svalbard (NYA 76.26°N 110.98°E geomagnetic) and Longyearbyen, Svalbard (LYR 75.31°N 111.88°E geomagnetic). Balmer α (Hα) with a natural wavelength of 6563Å was detected at Ny-Ålesund, while Balmer β (Hβ) at 4861Å was measured at Longyearbyen. The emissions are well known to originate from precipitating protons whose charge exchanges with the neutral atmosphere lead to a diffuse, Doppler-shifted emission region. Measurements are made using Ebert–Fastie spectrometers that are located 118 km apart on a line of roughly constant geomagnetic longitude, thus making this configuration suitable for studying the variation of proton energy with geomagnetic latitude, the so-called “velocity filter” effect. For two different days, analysis of the spectrometer data sets was performed, yielding in both cases positive energy differences between LYR and NYA in support of the velocity filter concept. To reduce uncertainties in the determined energies obtained from the Doppler profile, distributions of energy difference were constructed using the entire time period (up to 2 h) for each case.PACS Nos.: 92.60.hw 94.20.Ac, 94.30.Aa

Dissociation and fragmentation of furan by electron impact

Dissociation and fragmentation processes that produce electronically excited atomic and molecular fragments, following electron impact excitation, have been studied in furan. The optical excitation technique has been employed over the electron incident energy range 15–95eV. Formation of excited hydrogen atoms H(n) in the n=4–10 states has been detected by observation of the Balmer series. The diatomic CH fragments are formed in the A2Δ, B2Σ− and C2Σ− electronic states and the C2 fragments in the d3Πg excited state. The appearance energies for the H(n=4) (Hβ line) and the CH(A2Δ) (A2Δ→X2Πr transition) fragments have been measured to be 20.7±0.4 and 19.0±0.3eV, respectively. Absolute emission cross sections have been also determined for the above two transitions in the electron energy range from the appearance energy thresholds up to 95eV. Possible dissociation and fragmentation processes are discussed.