Continuum Theory of theU2Center in Alkali Halides

Various available spatially dependent dielectric-constant functions are use to calculate the $1s-2p$ transition energies of neutral hydrogen in KCl. The most reasonable dielectric functions seem to be those which use $k$-dependent dielectric constants to describe the electronic polarization of the crystals. The $1s-2p$ transition energies calculated in this manner agree well with the observed $U_2$ bands, while retaining the nearly free-hydrogenic nature of ground-state wave function, and thus provide an alternative to the transferred-electron model of the $U_2$ band due to Kerkhoff, Martienssen, and Sander.