Associative detachment in low-energy collisions between hydrogen atoms and atomic halogen anions

2001 ◽  
Vol 34 (6) ◽  
pp. 983-1004 ◽  
Author(s):  
M Cízek ◽  
J Horácek ◽  
F A U Thiel ◽  
H Hotop
Keyword(s):  
Low Energy ◽  
Hydrogen Atoms

Influence of low-energy electron beam irradiation on defects in activated Mg-doped GaN

2002 ◽  
Vol 744 ◽  
Author(s):  
O. Gelhausen ◽  
M. R. Phillips ◽  
H. N. Klein ◽  
E. M. Goldys
Keyword(s):  
Electron Beam ◽  
Electron Beam Irradiation ◽  
Low Energy ◽  
Energy Electron ◽  
Beam Irradiation ◽  
Hydrogen Atoms ◽  
Acceptor Pair ◽  
Low Energy Electron ◽  
The Impact ◽  
Mg Doped

ABSTRACTCL spectroscopy studies at varying temperatures and excitation power densities as well as depth-resolved CL imaging were conducted to investigate the impact of low energy electron beam irradiation (LEEBI) on native defects and residual impurities in metal-organic vapor phase epitaxy (MOVPE) grown Mg-doped p-type GaN. Due to the dissociation of (Mg-H)0 complexes, LEEBI significantly increases the (e,Mg0) emission (3.26 eV) at 300 K and substantially decreases the H-Mg donor-acceptor-pair (DAP) emission (3.27 eV) at 80 K. In-plane and depth-resolved CL imaging indicates that hydrogen dissociation results from electron-hole recombination at H-defect complexes rather than heating by the electron beam. The dissociated hydrogen atoms associate with nitrogen vacancies, forming a deeper donor, i.e. a (H-VN) complex. The corresponding deeper DAP emission with Mg centered at 3.1 eV is clearly observed between 160 and 220 K. Moreover, a broad yellow luminescence (YL) band centered at 2.2 eV is observed in MOVPE-grown Mg-doped GaN after LEEBI-treatment. It is suggested that a combination of LEEBI-induced Fermi-level downshift due to Mg-acceptor activation and simultaneous dissociation of gallium vacancy-impurity complexes, i.e. (VGa-H), is responsible for the observed YL.

Electron screening in low energy scattering of muonic hydrogen on hydrogen atoms

1986 ◽  
Vol 4 (2) ◽  
pp. 153-160 ◽  
Author(s):  
A. Adamczak ◽  
V. S. Melezhik ◽  
L. I. Menshikov
Keyword(s):  
Muonic Hydrogen ◽  
Low Energy ◽  
Electron Screening ◽  
Hydrogen Atoms ◽  
Energy Scattering

scholarly journals Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen

2019 ◽  
Vol 625 ◽  
pp. A78 ◽  
Author(s):  
A. M. Amarsi ◽  
P. S. Barklem
Keyword(s):  
Charge Transfer ◽  
Neutral Hydrogen ◽  
Stellar Atmospheres ◽  
Low Energy ◽  
Rate Coefficients ◽  
Collision Dynamics ◽  
Hydrogen Atoms ◽  
Stellar Spectra ◽  
Zero Rate ◽  
Excitation Processes

Low-energy inelastic collisions with neutral hydrogen atoms are important processes in stellar atmospheres, and a persistent source of uncertainty in non-LTE modelling of stellar spectra. We have calculated and studied excitation and charge transfer of C I and of N I due to such collisions. We used a previously presented method that is based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions for the adiabatic potential energies, combined with the multichannel Landau-Zener model for the collision dynamics. We find that charge transfer processes typically lead to much larger rate coefficients than excitation processes do, consistent with studies of other atomic species. Two-electron processes were considered and lead to non-zero rate coefficients that can potentially impact statistical equilibrium calculations. However, they were included in the model in an approximate way, via an estimate for the two-electron coupling that was presented earlier in the literature: the validity of these data should be checked in a future work.

First Microscopic Observation of Cadmium-Hydrogen Pairs in GaN

1996 ◽  
Vol 449 ◽  
Author(s):  
A. Burchard ◽  
M. Deicher ◽  
D. Forkel-Wirth ◽  
E. E. Haller ◽  
R. Magerle ◽  
...  
Keyword(s):  
Angular Correlation ◽  
Microscopic Observation ◽  
Correlation Spectroscopy ◽  
Low Energy ◽  
Hydrogen Atoms

ABSTRACTThe formation and properties of acceptor-hydrogen pairs in GaN have been studied using radioactive 111mCd acceptors and the perturbed γγ angular correlation spectroscopy (PAC). After H-loading by low energy implantation (100 eV) at temperatures between 295 K and 473 K, the formation of two Cd-H complexes involving about 30% of the Cd-acceptors is observed. The complexes have been identified as single hydrogen atoms bound to the Cd acceptor in two different configurations. The dissociation enthalpies of these configurations have been determined as 1.1(1) eV and 1.8(1) eV, respectively.

scholarly journals Production of atomic hydrogen by cosmic rays in dark clouds

2018 ◽  
Vol 619 ◽  
pp. A144 ◽  
Author(s):  
Marco Padovani ◽  
Daniele Galli ◽  
Alexei V. Ivlev ◽  
Paola Caselli ◽  
Andrea Ferrara
Keyword(s):  
Cosmic Rays ◽  
Atomic Hydrogen ◽  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Dissociation Rate ◽  
Low Energy ◽  
Hydrogen Atoms ◽  
Dark Clouds

Context. Small amounts of atomic hydrogen, detected as absorption dips in the 21 cm line spectrum, are a well-known characteristic of dark clouds. The abundance of hydrogen atoms measured in the densest regions of molecular clouds can only be explained by the dissociation of H2 by cosmic rays. Aims. We wish to assess the role of Galactic cosmic rays in the formation of atomic hydrogen, for which we use recent developments in the characterisation of the low-energy spectra of cosmic rays and advances in the modelling of their propagation in molecular clouds. Methods. We modelled the attenuation of the interstellar cosmic rays that enter a cloud and computed the dissociation rate of molecular hydrogen that is due to collisions with cosmic-ray protons and electrons as well as fast hydrogen atoms. We compared our results with the available observations. Results. The cosmic-ray dissociation rate is entirely determined by secondary electrons produced in primary ionisation collisions. These secondary particles constitute the only source of atomic hydrogen at column densities above ~1021 cm−2. We also find that the dissociation rate decreases with column density, while the ratio between the dissociation and ionisation rates varies between about 0.6 and 0.7. From comparison with observations, we conclude that a relatively flat spectrum of interstellar cosmic-ray protons, such as suggested by the most recent Voyager 1 data, can only provide a lower bound for the observed atomic hydrogen fraction. An enhanced spectrum of low-energy protons is needed to explain most of the observations. Conclusions. Our findings show that a careful description of molecular hydrogen dissociation by cosmic rays can explain the abundance of atomic hydrogen in dark clouds. An accurate characterisation of this process at high densities is crucial for understanding the chemical evolution of star-forming regions.

Spin-exchange scattering cross sections for hydrogen atoms at low temperatures

1980 ◽  
Vol 58 (6) ◽  
pp. 881-885 ◽  
Author(s):  
A. J. Berlinsky ◽  
B. Shizgal
Keyword(s):  
Cross Sections ◽  
Low Temperatures ◽  
Atomic Hydrogen ◽  
Spin Exchange ◽  
Low Energy ◽  
Energy Limit ◽  
Hydrogen Atoms ◽  
Exchange Scattering ◽  
Scattering Cross Sections

Calculations are presented of the low energy (0 < E ≤ 10−2 eV) spin exchange and frequency shift cross sections for (H,H) scattering, and of their thermal averages for 0 < T < 10 K. In particular, the behaviour of the cross sections in this low energy limit and the role of resonances due to orbiting collisions is studied in detail. A comparison is made with recent nmr measurements on gaseous atomic hydrogen at liquid helium temperatures. The results of this work suggest further useful experiments at low temperatures.

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