Measurement of cross sections for excitation of the 2P states of atomic hydrogen by charge-exchange collisions of protons in argon and nitrogen
Abstract
Absolute cross sections for the excitation of the 2P states of atomic hydrogen in charge-exchange collisions of protons in argon and nitrogen were measured by observing the Lyman-α radiation emitted in transitions from this state. Because of the lack of light standards in the vacuum ultraviolet region of the spectrum, the major problem of the measurements was the absolute calibration of the Lyman-α photometer. This calibration was obtained from coincidence measurements of Hα and Lyman-α photons in the presence of an electric field. The measurements were corrected for the effect of Doppler shift on the photometer sensitivity. For the evaluation of the coincidence measurements, the branching ratio of Hα transitions to the 2S state and the polarization of Lyman-α radiation, emitted in cascade processes, were needed. These quantities were obtained from quantum-mechanical calculations for a hydrogen atom in a weak electric field. Cross sections for the 2P states were obtained in the energy range from 0.5 to 30 keV. The 2P cross sections in argon had maxima of 2.34 × 10-17 and 2.84 × 10-17 cm2 at 3.35 and 11.86 keV, respectively, and in N2 maxima of 2.17 × 10-17 and 2.10 × 10-17 were observed at 3.39 and 11.3 keV, respectively. The energy dependence of the measured cross sections is in agreement with that of published measurements. Differences in the absolute values are discussed.
- Publication:
-
Physical Review A
- Pub Date:
- August 1975
- DOI:
- 10.1103/PhysRevA.12.460
- Bibcode:
- 1975PhRvA..12..460S
- Keywords:
-
- Atomic Excitations;
- Charge Exchange;
- Hydrogen Atoms;
- Proton Beams;
- Scattering Cross Sections;
- Argon;
- Atomic Energy Levels;
- Electron Orbitals;
- Electron Transitions;
- Lyman Alpha Radiation;
- Nitrogen;
- Particle Collisions;
- Ultraviolet Spectra;
- Atomic and Molecular Physics