Photodissociation of impurity-doped solids involving chemical reactions with host atoms is experimentally studied. We demonstrate that the formation of intermediate molecules (HKrCl) plays a central role in the photodissociation of HCl in solid Kr, developing considerably the general understanding of solid-state photolysis dynamics. In addition, these experiments provide a quantitative test for the ab initio calculations of IR absorption intensities of novel rare-gas molecules. The measured UV absorption spectrum of HKrCl is valuable for characterizing the electronically excited states of rare-gas containing species, which is a significant challenge to theory.