Penning ionisation of Na, K, Rb and Cs by He(23S1) in a stationary afterglow
- 14 March 1978
- journal article
- Published by IOP Publishing in Journal of Physics B: Atomic and Molecular Physics
- Vol. 11 (5) , 927-933
- https://doi.org/10.1088/0022-3700/11/5/025
Abstract
The rate of destruction of helium atoms in the metastable 23S1 state has been measured in a stationary helium afterglow containing either Na, K, Rb, or Cs. Any change in the destruction rate of He(23S) atoms when the alkali atom density is varied is attributed to Penning ionisation of the ground state alkali atoms. The measured rate coefficients in units of 10-10 cm3 s-1 are k(Na)=5.1+or-1.0, k(K)=7.7+or-1.5, k(Rb)=12.0+or-2.4, and k(Cs)=4.5+or-0.9. The corresponding Penning ionisation cross sections in units of 10-16 cm2 and for a temperature of about 350K are sigma (Na)=33+or-6, sigma (K)=55+or-10, sigma (Rb)=93+or-18, and sigma (Cs)=34+or-7. It is suggested that energy transfer from He(23S) to a core-excited autoionising state of K or Rb results in larger cross sections for these two alkalis.Keywords
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