Collisions Of Hydrogen Atoms Research Articles

Molecular theory of atomic collisions: A generalized perturbed stationary states approach

The perturbed stationary states equations, which describe low velocity atomic/ionic collisions using continuum states of the aggregate molecule have been generalized to include the effects of electron translation. The generalized nuclear scattering equations reduce to those of the perturbed stationary states method as the electron mass tends to zero. As either nuclear charge tends to zero, the solutions describe the translation of a free atom. The extraction of the proper T−matrices from the nuclear scattering solutions is a major difficulty in the molecular description of atomic collisions since molecular coordinates are not asymptotically appropriate. To this end we have examined asymptotic limits of the Fadeev equations, written in terms of potentials rather than the usual transition operators, to obtain the proper scattering boundary conditions and expressions for the inelastic, rearrangement and ionization T−matrices The theory is to be applied to charge transfer reactions involving low velocity collisions of hydrogen atoms with multiply charged ions.

Different forms of direct-and exchange-scattering amplitudes for then1s−n2stransition in electron-hydrogen collisions

A simple series-expansion form for the direct-scattering amplitude (involving real quantities) ${T}_{{n}_{1}s\ensuremath{-}{n}_{2}s}^{d}$ is given in the case of the ${n}_{1}s\ensuremath{-}{n}_{2}s$ transition in the electron---hydrogen-atom collision. Another form for ${T}_{{n}_{1}s\ensuremath{-}{n}_{2}s}^{d}$, consisting of few terms, is derived when the initial-state quantum number ${n}_{1}$ is small. When the quantum numbers ${n}_{1}$ and ${n}_{2}$ are very large, the dominant part of ${T}_{{n}_{1}s\ensuremath{-}{n}_{2}s}^{d}$ can be reduced to a single oscillatory trigonometric term, and this leads to some interesting features of the differential cross section. Simple integral forms for ${T}_{{n}_{1}s\ensuremath{-}{n}_{2}s}^{d}$ in the above-mentioned cases are also given. Expressions are further obtained for the exchange-scattering amplitude ${T}_{{n}_{1}s\ensuremath{-}{n}_{2}s}^{\mathrm{ex}}$, which includes terms of orders $O({\ensuremath{\beta}}_{0}^{\ensuremath{-}1})$ and $O({\ensuremath{\beta}}_{0}^{\ensuremath{-}2})$, with ${\ensuremath{\beta}}_{0}={k}_{1}^{2}+{n}_{2}^{\ensuremath{-}2}={k}_{2}^{2}+{n}_{1}^{\ensuremath{-}2}$, where ${k}_{1} ({k}_{2})$ is the initial (final) electron momentum. We also derive exact expressions for ${T}_{2s\ensuremath{-}2s}^{\mathrm{ex}}$ and ${T}_{1s\ensuremath{-}3s}^{\mathrm{ex}}$. All calculations are done in the first Born approximation.

Determination of high-npartial transfer cross sections in bare-nucleus—hydrogen-atom collisions

A method is proposed to determine partial cross sections for transfer into high-$n$ projectile shells in collisions between highly charged ions and atoms at energies around the energy of maximum transfer. Starting from the semiclassical close-coupling method with atomic-orbital basis sets, each group of orbitals belonging to a particular high-$n$ shell is coupled separately to those orbitals which dominate the capture process. Partial transfer cross sections ${\ensuremath{\sigma}}_{\mathrm{nl}}$ are calculated for ${\mathrm{C}}^{6+}$+H, ${\mathrm{N}}^{7+}$+H, and ${\mathrm{O}}^{8+}$+H collisions at 4-25 keV/amu with quantum numbers $n$ labeling shells up to those from which visible transitions take place.

Energy transfer in oxygen-hydrogen collisions

A formula is obtained for the rate coefficient for the production of a particle with a specific energy in an elastic collision with the atoms of a thermal gas. Accurate calculations are carried out of the energy transfer in elastic collisions of oxygen and hydrogen atoms. The fractions of hydrogen atoms with sufficient energy to escape from Venus produced in collisions of oxygen atoms with energies of 2.6 eV in a gas of atomic hydrogen at 100, 200 and 300 K are respectively 5.1, 6.9 and 8.5%. The mutual diffusion coefficient D of oxygen and hydrogen atoms is obtained. It can be represented by Dn = 7.25 × 10 17 T 0.71 cm −1 s −1 where n is the total atom density and T is the temperature.

Total and partial cross sections for electron capture in collisions of hydrogen atoms with fully stripped ions

Systematic investigations of charge-transfer reactions H/sup +/+A/sup( Z/-1)+(n,l) (A/sup Z/+) being a fully stripped ion) within the multichannel Landau-Zener theory with rotational coupling included (MLZRC) are presented. Total cross-section (sigma) calculations in the energy region 0.03--80 keV/amu for selected projectiles with charges 5< or =Z< or =74 are performed. Oscillations in the Z dependence of sigma are observed at low collision energies in the low-Z region. Above this region the Z dependence of sigma is linear. The n,l distributions of captured electrons are investigated and results for the partial cross sections sigma/sub n/ for a number of reactions are presented. The maxima of n distributions appear at n/sub m/roughly-equalZ/sup 3/4/ (in accordance with other theoretical predictions) and have a weak velocity dependence. Validity and limitations of the MLZRC model and the obtained results are discussed.

Ionization of hydrogen and deuterium atoms in thermal energy collisions with state-selected Ne(3s 3 P 2,3 P 0) metastable atoms

High resolution energy spectra of electrons and ions resulting from thermal energy collisions of hydrogen and deuterium atoms with state-selected metastable Ne(Ne(3s 3 P 2,3 P 0) atoms are reported. The electron spectra for Ne(3 P 2)+H(D) are very broad: The high energy part due to formation of NeH+ (NeD+) bound states (associative ionization), amounts to about 30% of the ionizing events, whereas the dominant part of the spectrum including a prominent low-energy peak is due to Penning ionization out of a strongly-attractive entrance potential curve. Comparison of the spectra with quantum mechanical fit calculations yields fairly accurate information on this potential, in particular its well depthD e [Ne(3 P 2)−H,D]= 2.0(1) eV. The spectra for Ne(3 P 0)+H, D are comparatively narrow with much lower cross sections than the one for the Ne(3 P 2) state. The corresponding entrance channel is a weakly bound van der Waals molecule with a well depth below 0.1 eV. A perturbation calculation of the Ne(3s)+H(1s) potential energy curves at large distances explains the observed difference between the Ne(3 P 2)+H(D) and Ne(3 P 0)+H(D) systems. Symmetry arguments are given that the major contribution to the Ne(3 P 2)+H(D) spectra is due to the2 Σ potential.

Translation factors in atomic collisions

AbstractDifferent methods proposed for taking into account the momentum transfer in electron capture collisions are reviewed. Exact one‐electron two‐Coulomb‐center molecular wave functions are considered for studying fully stripped ions–hydrogen atom collisions. The semiclassical impact parameter treatment is used, since it is well adapted to the keV/amu energy range investigated.

Use of the space-translation method in atomic collision problems

Invoking simple considerations based on properties of the unitary transformations, we show that the proper use of the Kramers-Henneberger space-translation method in atomic-collision problems gives essentially the same results as the conventional treatments and removes the ambiguities reported in the literature. Laser-assisted electron--hydrogen-atom collisions are considered as an example.

Erratum: Theory of electron—hydrogen-atom collisions in the presence of a laser field

Erratum: Theory of electron—hydrogen-atom collisions in the presence of a laser field

Erratum: Theory of electron - hydrogen-atom collisions in the presence of a laser field

Erratum: Theory of electron - hydrogen-atom collisions in the presence of a laser field

A study of the diffuse interstellar gas near the Pleiades

view Abstract Citations (24) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A study of the diffuse interstellar gas near the Pleiades Federman, S. R. Abstract Interstellar gas toward the Pleiades was studied by observing lines of CH, CH+, and K I along three lines of sight, taking the equivalent width, velocity at line center in the local standard of rest, and the Doppler parameter. Evidence for a shock of 10-15 km/s could be seen in the 3-4 km/s blueshift of the CH line relative to the CH+ line toward 20 Tau, the largest shock yet observed in a survey of CH and CH+ in diffuse interstellar clouds. Toward nu Tau, the narrow K I feature indicated a weak shock. Using the ratio r of atomic species with low ionization potentials to molecular hydrogen, the distance of the gas to the stars is found to be about 0.3 pc. This distance is inconsistent with the observed distribution of molecular hydrogen among its rotational levels, but the discrepancy is eliminated by considering collisions of atomic hydrogen with molecular hydrogen to be responsible for the distribution. Publication: The Astrophysical Journal Pub Date: February 1982 DOI: 10.1086/159662 Bibcode: 1982ApJ...253..601F Keywords: Astronomical Spectroscopy; Gaseous Diffusion; Interstellar Gas; Line Spectra; Molecular Ions; Pleiades Cluster; Star Clusters; Astronomical Models; Gas Density; Interstellar Extinction; Molecular Rotation; Molecular Spectra; Monatomic Gases; Potassium; Radicals; Stellar Evolution; Astrophysics full text sources ADS |

Studies on atom–triatom reactive scattering. Classical dynamics of H + C2H collisions

The classical dynamics of the collisions of hydrogen atoms with C2H has been studied using a six-dimensional potential-energy surface for the ground state of C2H2. At low collision energies complexes are formed which have predominantly acetylene rather than vinylidene geometries. The estimated rate constant for this recombination reaction is 100 times larger than a published value determined by transition-state theory.

Electron-loss cross sections for collisions of normal and metastable hydrogen atoms with atomic hydrogen, using four-body trajectory calculations

Four-body trajectory calculations are presented for collisions of $\mathrm{H}(1s)$ and $\mathrm{H}(2s)$ atoms with atomic hydrogen. Since none of the ${\mathrm{H}}^{\ensuremath{-}}$ formations was found to be classically stable, only cross sections for electron loss due to direct and exchange processes are presented. Where comparable ionization cross sections are not available in the Born and classical impulse approximations, fresh calculations have been carried out. The various cross sections are compared among themselves and with available experimental data.

Angular and energy distribution of electrons from 15- to 150-keVH0+He collisions

An electrostatic analyzer positioned at various angles has been used to measure absolute values of cross sections for electron production in collisions of neutral hydrogen atoms with helium as a function of the angle and energy of the ejected electrons. These cross sections are compared with corresponding ones for proton and electron impact to infer the mechanisms of electron production. A prominent peak in the energy distribution due to electron loss from the projectile occurs at an electron velocity equal to that of the projectile. At very low electron energies the similarity of the energy distribution to that due to electron impact suggests that the large cross section there is due to ionization of the target by the electron carried by the projectile. As with proton impact, the cross sections at low projectile velocities fall off approximately exponentially with the energy of the ejected electron, in agreement with the predictions of the electron promotion model.

H(2s)Formation and the Lyman-αPolarization in 1-7-keVH+-H Collisions

A multistate molecular approach to the proton--hydrogen-atom collision is formulated. Spurious long-range couplings are avoided and Galilean invariance enforced through variationally determined momentum translation factors. Well-defined radial and rotational couplings are employed in the 1--7-keV energy range in a ten-state calculation. Good agreement with Bayfield is obtained for the 2s charge-exchange probability. Concerning polarization of Lyman-..cap alpha.. radiation, comparison with Kauppila et al. is made.

Electron – hydrogen atom collision in the presence of a circularly polarized laser field

Electron–hydrogen collision in the presence of a circularly polarized laser field is studied within a formalism based in an appropriate space-translations transformation and the Green's function formalism. The Born–Oppenheimer approximation for the scattering amplitude is obtained and the dependence of the differential and total excitation cross section on the electromagnetic field polarization is studied.

Electron capture, loss and collisional destruction of 5-26 keV metastable and ground-state hydrogen atoms in collisions with atomic and molecular hydrogen

A tungsten-tube furnace containing highly dissociated hydrogen has been used, in conjunction with a technique previously used in this laboratory, to determine cross sections for collisional destruction, electron loss and electron capture by fast hydrogen metastable atoms in atomic hydrogen. Cross sections are not more than about 65% of the corresponding cross sections in H2. While electron loss cross sections for H(2s) atoms are found to be considerably greater than those for H(1s) atoms, corresponding electron capture cross sections are not greatly different. Theoretical estimates of cross sections for collisional destruction and electron loss by H(2s) atoms in H are in poor accord with the present measurements.

Differential and total cross sections in 1+7 keV proton+hydrogen atom collisions

Extensive calculations have been carried out on differential and total cross sections for H(2s) and H(2p) production in low-energy proton-hydrogen-atom collisions. A multi-state molecular PSS approximation was adopted with the inclusion, up to second order for velocity terms, of the variationally determined translational factors of Crothers and Hughes (1978). Results presented here illustrate the importance of radial couplings in close collisions, the effect of which has often been underestimated. The authors also highlight the discrepancies which still persist between theory and experiment in the total cross section for capture into the 2s state of hydrogen below 7 keV.

1s-2s excitation of fast hydrogen atoms in collisions with atomic and molecular hydrogen

Cross sections for 1s-2s excitation of 2-25 keV hydrogen atoms in passage through H and H2 have been determined. A tungsten-tube furnace has been used to provide a target of highly dissociated hydrogen and fast H(2s) metastable atoms formed in the excitation process have been detected by recording the Lyman- alpha quench radiation induced by an electric field. Measured cross sections in H are found to be in generally poor accord with theoretical estimates.

Electron—hydrogen-atom collisions in the presence of a laser field: Born-Oppenheimer approximation

The collision of an electron and a hydrogen atom in the presence of a laser field is studied within a previously proposed approximation (based on the space-translation approximation) for the bound states of the hydrogen atom. The Green's-function formalism is applied to derive an expression for the scattering amplitude associated to multiphoton processes. The Born-Oppenheimer approximation is obtained and numerical calculations are performed for the 1s ..-->.. 2s inelastic excitation. It is shown as expected that exchange effects are important only for scattering processes involving low-energy electrons.