Internal ionization of Ar and Kr noble-gas cryocrystals by the excitation energy of trapped metastable excited atoms

Abstract

Local metastable excited states are found in Ar and Kr cryocrystals when He gas-discharge products are trapped in the growing cryocrystals. These states are detected by ESR and are interpreted as being local metastable excited np5(n+1)s3P2 atomic-type states in Ar and Kr cryocrystals. The study showed that the yield of the 3P2 excitations in the above process decreases with increasing temperature. Analysis of the results allows the following explanation of the observed effect to be given. Metastable excited He atoms from the He gas discharge are trapped in the growing Ar or Kr cryocrystals and transfer their excitation energy to the cryocrystal to form, in the process of internal ionization, a RG+ ion and a free electron in the conduction band, whereupon the fast (10-12 s) self-trapping reaction of a hole follows: RG+RG to RG2+. Thereafter either the dissociative recombination reaction RG2++e to RG2** to RG+RG*(3P2) or recombination RG2++e to RG+RG to produce ground-state atoms could take place. The former is likely at lower temperatures, and the latter at higher temperatures when the vibrational relaxation rate of the RG+ molecular ion increases and the mobility of free electrons in the conduction band decreases. This is the reason for the observed temperature dependence.