Excited States of theFCenter in LiCl

Abstract

Excited states of the $F$ center have been seen by Lüty 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 $3.14\left(F\right)\mathrm{}$, $3.92\left(K\right)\mathrm{}$, $4.76-4.86\left(L_1{L}_2\right)$, and $6.14\left(L_3\right)$. 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 $2.14\left(R_2\right)$, $2.72\left(R_1\right)$, $3.30\left(F\right)\mathrm{}$, $4.52\left(L_1\right)$, $4.95\left(L_2\right)$, $5.43\left(L_3\right)$, and $5.75\left(L_4\right)$. 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.