Born and impact-parameter cross sections for the process H(1s) + H(1s) → H(2s) + H(1s)

1988 ◽  
Vol 66 (7) ◽  
pp. 645-648 ◽  
Author(s):  
R. Mayo ◽  
S. Rolston ◽  
T. J. Morgan
Keyword(s):  
Impact Parameter ◽  
Cross Sections ◽  
Infinite Order ◽  
Neutral Hydrogen ◽  
Equation Of Motion ◽  
Parameter Method ◽  
Hydrogen Atoms ◽  
First Order ◽  
Straight Line ◽  
Neutral Ground

We report the results of a series of calculations of the cross section for the excitation of a neutral hydrogen atom to the 2s level, due to the collision of two neutral ground-state hydrogen atoms within the energy range 1–100 keV. Cross sections are presented for the first-Born approximation and for the straight-line impact-parameter method employing velocity truncation approximations. Electron exchange terms have been included in all calculations. Reported impact-parameter calculations are the best results of a series of calculations studying the inclusion, in the equation of motion, of terms that are zero- and first-order in the internuclear velocity. These results are compared with first- and second-order Born calculations neglecting exchange, recent infinite-order impact-parameter calculations, and experimental data.

scholarly journals NLTE Effects on Oxygen Lines

2002 ◽  
Vol 12 ◽  
pp. 429-431 ◽  
Author(s):  
Dan Kiselman
Keyword(s):  
Cross Sections ◽  
Neutral Hydrogen ◽  
Line Formation ◽  
Collisional Excitation ◽  
Hydrogen Atoms ◽  
Molecular Line ◽  
Oxygen Abundance ◽  
Solar Type

AbstractThe NLTE effects affecting oxygen-abundance determinations of solar-type stars are discussed. LTE is safe for the forbidden lines. The permitted triplet at 777 nm is expected to show NLTE effects so that assuming LTE overestimates the abundance, but the magnitude of the effects is dependent on the poorly known cross sections of collisional excitation by collisions with neutral hydrogen atoms. Little is known about the NLTE effects on molecular line formation.

First-order exchange approximation

1963 ◽  
Vol 276 (1366) ◽  
pp. 346-353 ◽  
Keyword(s):  
Elastic Scattering ◽  
Cross Sections ◽  
Born Approximation ◽  
Scattering Amplitude ◽  
Wave Functions ◽  
Hydrogen Atoms ◽  
Final State ◽  
First Order ◽  
Exchange Approximation ◽  
Exchange Scattering

It is shown that when the Born approximation is applied to rearrangement collisions in the customary way, terms of the first order in the interaction energy between the colliding particles are omitted from the exchange scattering amplitude. If these terms are retained the arbitrariness which arises from the lack of orthogonality between the initial and final state wave functions is removed. The first-order exchange approximation derived in the present paper is employed to calculate the cross-sections for the 1 s -2 s and 1 s -2 p excitations of hydrogen atoms by electron impact and the elastic scattering of electrons by hydrogen atoms.

Impact parameter treatments of certain hydrogen-proton and hydrogen-hydrogen excitation collisions

1958 ◽  
Vol 245 (1242) ◽  
pp. 299-311 ◽  
Keyword(s):  
Impact Parameter ◽  
Stationary State ◽  
Born Approximation ◽  
Order Approximation ◽  
Hydrogen Atoms ◽  
First Order ◽  
Normal Hydrogen ◽  
First Order Approximation ◽  
The Impact

Consideration is given to the impact parameter form of the Born approximation and of the pRA approximation (i.e. the first-order approximation to which the perturbed stationary state, or PSS, approximation tends). Calculations are carried out on the excitation of normal hydrogen atoms to the 2 s or 2 p states in encounters with protons and other normal hydrogen atoms. The results obtained provide some information on the range of validity of the Born approximation. The impact-parameter treatment corresponding to a simplified version of the second Born approximation is given and discussed. Attention is drawn to the fact that for certain transitions the pRA approximation fails seriously when the encounter is very close.

Vacuum ultraviolet emissions of trifluoromethane following electron impact in the wavelength range 50–130 nm

1989 ◽  
Vol 67 (7) ◽  
pp. 694-698 ◽  
Author(s):  
Shouye Wang ◽  
J. W. McConkey
Keyword(s):  
Electron Impact ◽  
Wavelength Range ◽  
Cross Sections ◽  
Incident Energy ◽  
Vacuum Ultraviolet ◽  
Neutral Hydrogen ◽  
Dissociative Excitation ◽  
Hydrogen Atoms ◽  
Threshold Excitation ◽  
Ultraviolet Emissions

The dissociative excitation of CF3H by electron impact has been studied under single collision conditions for incident energies up to 600 eV. The emission spectrum in the wavelength range 50–130 nm shows many features arising from neutral and singly ionized fluorine and carbon fragments, as well as from neutral hydrogen atoms. Absolute cross sections for the observed features were measured at 200 eV incident energy, while the excitation functions of the most intense emissions were studied over the whole energy range. The threshold excitation of the hydrogen Lyman α line displays onsets at 18.4 and 34.0 eV, while that of the fluorine F I 95.5 nm feature shows only one onset at 33.0 eV. Possible dissociation channels are discussed.

Lyman–α excitation and resonant charge exchange in slow H+–H(1s) collisions

1970 ◽  
Vol 48 (3) ◽  
pp. 313-329 ◽  
Author(s):  
Stephen K. Knudson ◽  
Walter R. Thorson
Keyword(s):  
Charge Exchange ◽  
Cross Sections ◽  
Hydrogen Atoms ◽  
Resonant Charge Exchange ◽  
Straight Line ◽  
Classical Path ◽  
Sensitive Function ◽  
Interference Oscillations ◽  
The Impact ◽  
Excitation Probability

The dominant processes in slow collisions (E < 0.5 keV) of protons and 1s hydrogen atoms are direct elastic scattering, resonant charge exchange, and direct and exchange excitations of H(2p). Differential cross sections have been calculated for all these events by both quantal and classical methods, and characteristics of the resulting Lyman–α (Ly–α) radiation determined.Significant differences from earlier calculations are found for excitation probability, polarization of Ly–α, and the interference oscillations in the charge exchange probability. The phase of the latter is a sensitive function of the interactions causing inelastic scattering. The source of discrepancy with earlier results is the use of the impact parameter approximation (straight-line trajectories); over the range of significant excitation probability, classical path methods using true trajectories give accurate inelastic parameters. Comparison of quantal and classical calculations shows that accurate results for all properties discussed can be obtained by combining classical path calculations of inelastic parameters with semi-classical phase shifts for pure elastic scattering.If polarizations calculated here are used to reinterpret earlier observations of Ly–α emission from 300 eV collisions, the resulting experimental cross sections are not inconsistent with the basic theoretical prediction of equal direct and exchange excitation probabilities.

scholarly journals Line Broadening Cross Sections for the Broadening of Transitions of Neutral Atoms by Collisions with Neutral Hydrogen

1998 ◽  
Vol 15 (3) ◽  
pp. 336-338 ◽  
Author(s):  
P. S. Barklem ◽  
S. D. Anstee ◽  
B. J. O'Mara
Keyword(s):  
Cross Sections ◽  
World Wide ◽  
Neutral Hydrogen ◽  
Spectral Lines ◽  
Line Broadening ◽  
End User ◽  
Hydrogen Atoms ◽  
Fortran Code ◽  
The World ◽  
Spectrum Synthesis

AbstractLine broadening cross sections for the broadening of spectral lines by collisions with neutral hydrogen atoms have been tabulated by Anstee & O'Mara (1995), Barklem & O'Mara (1997) and Barklem, O'Mara & Ross (1998) for s–p, p–s, p–d, d–p, d–f and f–d transitions. To make these data more accessible to the end user, fortran code which interpolates in these tabulations has been prepared and placed on the World Wide Web. It should be easy to incorporate this code into existing spectrum synthesis programs or to use it in a stand-alone mode to compute line broadening cross sections for specific transitions. The use of the code is demonstrated by its application to two transitions of astrophysical interest.

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