Collisional Relaxation Processes for the n=3 States of Helium. II. Associative Ionization
- 1 February 1972
- journal article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 56 (3) , 1077-1082
- https://doi.org/10.1063/1.1677281
Abstract
Rate constants for the associative ionization reaction He * + He → He 2 + + e have been measured, where He* represents the n=3 states of helium. By line absorption from the metastable 21S and 23S states, the n=3 states in the positive column of a dc discharge in helium were selectively and periodically modulated. Using phase-sensitive detection, the changes in excited-state populations were determined spectroscopically while the corresponding in-phase variations in the concentration of He 2 + were measured with a quadrupole mass filter. The cross sections for associative ionization in units of 10−16 cm2 were determined to be: σ (3 3 P) = 1.6 ± 0.1, σ (3 1 P) = 3.1 ± 1, σ (3 3D) = 4.5 ± 0.5, and σ (3 1D) = 20 ± 4. σ (3 3S) and σ(31S) were apparently zero.Keywords
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