H(2s) formation in H/sup +/-H and H-H collisions
Cross sections for metastable H(2s) formation by electron capture in H/sup +/-H(1s) collisions and by excitation in H(1s)-H(1s) collisions have been measured over the energy range 1.9--92 keV. A fast beam of H/sup +/ ions or H(1s) atoms was passed through a tungsten-tube-furnace target which contained thermally dissociated hydrogen. Fast metastable H(2s) atoms formed by collisions in the target were detected downstream using electric field quenching and Lyman-..cap alpha.. photon-counting techniques. The present values are normalized at 24.5 keV to the average value of three previous independent measurements of the H(2s) formation cross section in H/sup +/-H collisions which agree to within 20%. Measured cross sections for both H/sup +/-H and H-H collisions contain only one maximum, in contrast with certain theoretical predictions. For H/sup +/-H the low-energy data are in good agreement with theoretical results based on a multistate molecular treatment of the collision. Above 75 keV the H/sup +/-H data agree with the Born approximation cross sections. Close-coupling pseudostate predictions lack overall detailed agreement with the present results, although the maximum in the cross section is reproduced well. High-energy (E>15 keV) coupled-state calculations using a scaled hydrogenic two-center expansion are in good accord with the data. For H-H collisions all theoretical treatments are in poor accord with the present experimental results. Above 40 keV the measured H-H cross section is inversely proportional to the impact energy. This E/sup -1/ energy dependence is in agreement with high-energy theoretical predictions. However, above 10 keV the Born approximation predicts structure in the cross section due to simultaneous excitation of the projectile and target which is not observed. The present results are compared with previous experimental determinations, and discrepancies are found to exist.
- Research Organization:
- Physics Department, Wesleyan University, Middletown, Connecticut 06457
- OSTI ID:
- 5122799
- Journal Information:
- Phys. Rev., A; (United States), Journal Name: Phys. Rev., A; (United States) Vol. 22:4; ISSN PLRAA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ATOM COLLISIONS
ATOM-ATOM COLLISIONS
ATOMIC BEAMS
BEAMS
CAPTURE
CATIONS
CHARGED PARTICLES
COLLISIONS
CROSS SECTIONS
ELECTRON CAPTURE
ELEMENTS
ENERGY LEVELS
ENERGY RANGE
EXCITED STATES
HYDROGEN
HYDROGEN IONS
HYDROGEN IONS 1 PLUS
ION BEAMS
ION COLLISIONS
ION-ATOM COLLISIONS
IONS
KEV RANGE
KEV RANGE 01-10
KEV RANGE 10-100
METASTABLE STATES
NONMETALS