Frenkel-like excitation

Atomic cryocrystals which are widely used as inert matrices in the matrix isolated spectroscopy become non-inert after excitation of an electronic subsystem. Local elastic and inelastic lattice deformation around trapped electronic excitations, population of antibonding electronic states during relaxation of the molecular-like centers, and excitation of the Rydberg states of guest species are the moving force of Frenkel-pairs formation in the bulk and desorption of atoms and molecules from the surface of the condensed rare gases. Even a tiny probability of exciton or electron-hole pair creation in the multiphoton processes under, e.g., laser irradiation has to be taken into account as it may considerably alter the energy relaxation pathways. 

The localization of the lowest-energy exciton in ionic solids like the alkali halides is such that neither the Frenkel nor Wannier approximation is valid. An early picture of the excitation by Hilsch and Pohl [58] was that absorption of a photon results in the transfer of an electron from one of the halogen ions to a neighboring alkali ion. This charge-transfer model of the exciton attributed observed double-absorption peaks to the spin-orbit splitting of the halide ion, and successfully predicted exciton energies by the empirical relation... 

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