Excited States of the F Center in LiCl

Excited states of the F center have been seen by L\"uty in potassium and rubidium halides at energies up to several volts above the usual F-center transition. A molecular-orbital calculation of the F center in LiCl has been made by Wood, using only the $2s$ and $2p$ orbitals of lithium. From the levels thus computed, his tentative assignment of energies in eV to bands is $3.14(F)$, $3.92(K)$, 4.76-4.86(L₁L₂), and 6.14(L₃). Experiments are reported on LiCl colored by x rays at room temperature, cooled to 4^∘{}K, measured, bleached with incandescent light, and remeasured. The bleaching spectrum shows bands that are thought to be 2.14(R₂), 2.72(R₁), $3.30(F)$, 4.52(L₁), 4.95(L₂), 5.43(L₃), and 5.75(L₄). On the basis of the model of Klick and Kabler, which views the L bands as involving the excitation of the alkali to higher atomic states, the lithium atomic levels would have to be compressed by about 45% to agree with experiment. This amount of compression, which is larger than that for the salts previously measured, may be connected with the large dielectric constant of LiCl.