Excited States Of Hydrogen Research Articles

Muon transfer in excited muonic hydrogen.

The cross sections and rates of muon transfer between excited states of muonic hydrogen are presented as functions of collision energy for different isotope combinations. Electron screening of the field of the target nucleus is taken into account. The ground-state population, ${\mathit{q}}_{1\mathit{s}}$, of muonic hydrogen is obtained for different collision energies, target densities, and relative hydrogen isotope concentrations, considering cascade processes for the principal quantum numbers n\ensuremath{\le}12. The obtained results for ${\mathit{q}}_{1\mathit{s}}$ are significantly smaller than the recent experimental data for D-T and H-D mixtures (tenfold and twice, respectively) and indicate that some new effects must be considered to improve the agreement.

Close-coupling calculations of electron capture cross sections from the n=2 states of H by protons and alpha particles

Cross sections for electron capture from the n=2 excited states of atomic hydrogen in collisions with protons and alpha particles are calculated using the semiclassical close-coupling method where the time-dependent wavefunction is expanded in terms of travelling atomic orbitals on each collision centre. The results are compared with existing close-coupling calculations in which molecular orbital expansions were used. The dependence of the total and partial electron capture cross sections on the alignment of the initial excited 2p states is examined.

Highly excited Rydberg states of hydrogen from a high-temperature diffusion source

The methods used for formation and observation of HR (highly excited Rydberg) states of alkali are here adopted for the study of hydrogen HR states. Electronically highly excited states are formed in a hydrogen-filled diffusion source with a graphite foil as emitter at high temperature. The excited states are detected by electrostatic methods, mainly by their interaction with a well shielded collector. Excited negative hydrogen and/or alkali ions are formed at the first grid in the analysing device, and give emission of electrons at the collector. The flux from the source can be cut off instantaneously with a beam flag, which reveals time constants of the order of minutes in the signal. It is concluded that surface layers of excited states are formed on the electrode surfaces. A condensed phase of electronically excited so-called Rydberg matter was predicted by Manykin et al. (1981, 1982) and reported by Aman et al. (1990) and Svensson et al. (1992) Aman et al. (1992) later reported on non-alkali Rydberg matter. A similar type of matter appears to be found in the present study.

Photodissociation dynamics of doubly excited Rydberg states of molecular hydrogen

We have applied photofragment ion imaging to investigate the dissociation dynamics of low-lying, doubly excited states of molecular hydrogen. A doubly excited electronic state is one in which both of the hydrogen electrons reside in excited molecular orbitals. Two-step, two-color multiphoton excitation of H2, first via 201.8 nm, two-photon excitation into the E, F 1Σ+g(vE=0, J=1) state, followed by ∼563 nm, 1+m (m=1, 2) excitation through the B″ 1Σ+u(v=0, J=0, 2), D 1Πu(v=2, J=1, 2), and B′ 1Σ+u(v=4, J=0, 2) states provides a ready means of populating several low-lying doubly excited states of H2 at increasing internuclear separations. From these doubly excited repulsive states, both dissociation and autoionization processes are possible. Because the excitation energy remains relatively constant as each intermediate state is accessed, differences in the photodissociation dynamics via each state can be ascribed directly to the effects of changing internuclear separation and electronic symmetry of the intermediate and dissociative states. H+ fragments detected from each photodissociation pathway are distinguished by their differing velocities, determined from an ion image.

Migration of energy in the hydrogen bonded chain of peptide groups

A theory is proposed for the nonlinear excited states in the hydrogen bonded chain of peptide groups, where the interaction between intramolecular and intermolecular vibrations is taken into account. It is an interpolation between the behaviour in two limiting cases, i.e. the vibron soliton in the subsonic region, and the acoustic soliton in the supersonic region. Using this framework, the mechanism of energy migration in hydrogen bonded systems of peptide groups is analysed.

Relativistic and nonrelativistic finite-basis-set calculations of low-lying levels of hydrogenic atoms in intense magnetic fields.

A finite-basis-set method is used to calculate relativistic and nonrelativistic binding energies of an electron in a static Coulomb field and in magnetic fields of arbitrary strength (0B\ensuremath{\le}${10}^{13}$G). The basis set is composed of products of Slater- and Landau-type functions, and it contains the exact solutions at both the Coulomb limit (B=0) and the Landau limit (Z=0). Relativistic variational collapse is avoided and highly accurate results are obtained with the basis set. The relativistic corrections obtained for intense magnetic fields (B\ensuremath{\gtrsim}${10}^{9}$G) differ from the previous relativistic calculations based on the adiabatic approximations. It is found that the sign of the relativistic correction changes from negative to positive near B\ensuremath{\approxeq}${10}^{11}$ G for the ground state and near B\ensuremath{\approxeq}${10}^{10}$ G for the 2${\mathit{p}}_{3/2}$(\ensuremath{\mu}=-3/2) excited state of hydrogen. The method is checked to be very accurate by means of the virial theorem, sum rules, and the relativistic low-B limit where comparison can be made with perturbation results. In the nonrelativistic limit of the Dirac equation, our results agree with other accurate nonrelativistic calculations available and with our own calculations based on the Schr\"odinger equation, which converge to more significant digits than previous calculations for the whole range of magnetic fields.

Charge exchange at grazing reflection of swift ions from a solid surface

Abstract Charge exchange at grazing reflection of a fast ion from a metal surface is studied in the semiclassical approximation. It is shown that in a certain range of ion speeds the resonance-tunneling electron capture occurs and as a result of polarization of the electrons of the metal charge exchange to excited states of hydrogen takes place and inversed population in the beam of atoms occurs.

Interplay of resonant and Auger processes in proton neutralization after grazing surface scattering

We present model calculations for proton neutralization after grazing reflection at an aluminum surface over a wide range of projectile velocities around the Bohr or Fermi velocity. The contribution of excited hydrogen states to the neutral fraction, as well as negative-ion formation can be regarded as small in this case. Both resonant and Auger electron capture from the metallic conduction band into the 1s ground state of hydrogen as well as electron loss by resonance and Auger ionization of the ground state are taken into account on equal footing within a rate-equation approach. As a consequence, our model allows to estimate, for the first time, the effect of the particle velocity parallel to the surface plane on the relative role of resonant and Auger-type electron transfer in ion-surface neutralization. The results of our theoretical model are compared with recent experimental data for grazing scattering of protons at an Al(111) surface.

Observation of doubly excited resonances in the H- ion.

Laser photodetachment on a relativistic H{sup {minus}} beam has revealed several series of resonances in which both electrons are excited. These bound states in the continuum'' appear as dips in the partial production cross sections of various excited states of neutral hydrogen. We present here a detailed account of the experimental observation of the resonances and the results of fits of the measured yields to sets of Fano profiles. A simple analytic formula for the energy-level spacing in this quantum-mechanical three-body system is verified.

Emission-line ratios at high densities

Photoionization calculations are used here to study the density dependence of important emission lines for nucleon densities significantly greater than those considered standard. It is found that strong permitted emission lines suffer depression of their emissivity due to photon trapping and collisional destruction. Hydrogen continuum emission and some weak lines of heavy elements become more prominent at n(e) greater than 10 to the 10th/cu cm as they become increasingly important coolants. At high density and column mass, the Balmer decrement flattens because of the significant population in excited states of hydrogen. The results suggest that high-density, large column mass clouds could contribute an appreciable fraction of the observed Balmer line flux.

Ionisation of the first excited state of hydrogen by bare ions at intermediate and high velocities

The continuum distorted-wave-eikonal initial-state model is extended to study ionisation of hydrogen atoms in arbitrary initial states by multiply charged ion impact. These results are used to study total cross sections as a function of the impact energy for ionisation of the first excited stage by proton impact. The dependence on the projectile charge is discussed and compared with results for the ionisation of the ground state and with predictions from the first Born approximation.

Nonperturbative ac Stark shifts in hydrogen atoms

The evolution of low excited states of hydrogen in the presence of a strong light field is investigated by using the complex dilatation method with a finite basis of Slater-type functions. The method is applied for wavelengths of 592, 608, and 616 nm, which have been investigated experimentally. The results of the calculation are in agreement with experimental observations as far as comparison is possible.

Formation of excited hydrogen states in stimulated desorption from an alkali-promoted surface.

The desorption of hydrogen from alkali-promoted surfaces has been studied with electron-stimulated desorption. Excited hydrogen states are found for work functions that are larger than the binding energies of the corresponding atomic levels. This finding is in direct contrast with the conventional image shift of neutral atomic levels near surfaces and indicates that the levels are instead downshifted near the surface. Calculations of the energy shift and broadening of atomic hydrogen levels in the vicinity of a potassium atom chemisorbed on a metal surface confirms such a downshift. A model is presented that accounts for the observed formation of excited H in ESD from alkali-promoted surfaces.

Influence of electric fields on highly excited states of H2: quantum-defect-theory approach

A quantum-defect theory of the Stark effect given recently by Sakimoto (1987) is applied to study the effects of an electric field on highly excited states of molecular hydrogen. The Stark energy levels are calculated. Also investigated are field effects on photoionisation through rotational autoionisation.

Orientation and alignment of collisionally excited atomic states.

The orientation and alignment parameters of atomic excited states of hydrogen and helium atoms formed in collisions with electrons, positrons, protons, and antiprotons are examined. For the orientation parameter 〈${L}_{y}$〉 (defined to be the expectation value of the electronic angular momentum perpendicular to the collision plane), it is found that the signs of 〈${L}_{y}$〉 for proton and positron impact are negative, consistent with the prediction of the classical model with a repulsive force. For electron and antiproton impact, except for electron scattering at large angles, the signs of 〈${L}_{y}$〉 are positive, consistent with the classical model with an attractive force. A simple semiempirical scaling of 〈${L}_{y}$〉 for electron-impact excitations to 2p states was found. The orientation of 2p states formed in electron capture in proton--hydrogen-atom collisions and in positron--hydrogen-atom collisions are also studied and the angular dependences of 〈${L}_{y}$〉 are found to show similar behavior. We also examine the orientation parameters for excitation and capture to 3d states and the alignment angles for excitation and capture to 2p states. It is found that in the latter cases these parameters do not show similar simple dependences with scattering angles.

The state multipoles of the n=2 state of atomic hydrogen

A determination of all the state multipoles of the n=2 excited state of atomic hydrogen has been made. The kinematical conditions were a crossed electron-atom-beam geometry in which the incident electron energy was 350 eV and the scattering angle 3'. The experimental technique measures the scattered 10.2 eV energy loss electrons in coincidence with the 10.2 eV photons from either the 2P state or the delayed Stark-quenched 2S-state decay. An external electrostatic field mixes the S and P states, permitting the observation of their coherence by measuring the linear and circular photon polarisations, while in-plane angular correlations for a zero electric field determine the P-state multipoles. The state multipoles were deduced from a least-squares fit of the measured data to the quantum mechanical expressions determined for a model of an S-P (mj=1/2) superposition excited state with averages over the singlet and triplet spin states.

Dissociation of doubly excited states of H 2 into Rydberg atoms

We report the dissociation of doubly excited states of molecular hydrogen into an excited and a ground-state atom. After three-photon excitations to various vibrational levels in the B 1Σ u + state, one- and two-photon excitations result in doubly excited states with a (2pσ u) core of both gerade and ungerade symmetry. For the first time, excitation of Q 1 states with all principal quantum numbers is observed. Dissociation of these states results in a complete Rydberg series of atomic fragments, which are photoionized. The energy of the photoelectrons is measured. The series is characterized by the lower states, which are energetically resolved up to n = 5, and the limit n → ∞ of the series.

Charge Exchange in Laboratory and Astrophysical Plasmas

AbstractRecent experiments in tokamak plasmas demonstrate that charge exchanges manifest themselves in a wide variety of situations. It is now realized that charge exchanges involving excited states of hydrogen should be considered: these reactions represent a challenge for atomic physics, detailed plasma modeling, and quantitative plasma diagnostics. Charge exchanges between ions can in some cases modify the state of the gas and produce specific emission.Charge exchanges are important for the ionization balance of many ions in either warm coronal plasmas or photoionized plasmas of Astrophysics. Lines produced by charge exchange have been discovered in the spectrum of nebulae and probably the solar chromosphere. Introduction of charge exchanges modifies earlier views about the structure of some astrophysical objects. The nebulae appear as valuable “laboratories” to check theoretical charge exchange cross sections at very low energy. It is suggested that the detection of charge exchange lines in the solar spectrum would provide new insights into the dynamics of the interface between the chromosphere and the corona. It is pointed out that charge exchanges between heavy particles may have significant effects in the ionization front of some nebulae.

Electron-photon correlations for e--H(12S1/2-32Pj, 32Dj) collisions

A consistent version of the distorted-wave Born approximation has been used to calculate the first electron photon angular correlation data associated with the electron excited 32Pj and 32Dj states in hydrogen. The results show good agreement when compared with the recent measurements of Chwirot and Slevin (1987).

Excitation transfer due to neutral collisions in excited states of atomic hydrogen

The H alpha Balmer line emitted by a low-excitation electrical discharge at liquid nitrogen and room temperatures has been studied with a Fabry-Perot interferometer. With partial resolution of the fine structure, the line profile was observed to depend on buffer gas composition, pressure, and temperature, but not on discharge current. Interferograms computed from the known fine structure and transition probabilities, with allowance for non-thermal populations in the excited substates, matched the observed profiles quite well. The populations deduced from these fits are shown to approach thermal equilibrium with increasing gas pressure in a way which allows the collisional excitation transfer from the 3p to 3d states to be determined. Data for H-H, H-He, and H-H2O collisions are presented.