The HCl (DCl)/Kr matrixes were irradiated at 193 nm, which produced matrix-isolated H (D) and Cl atoms as permanent photolysis products. The annealing-induced formation of HKrCl and DKrCl was used as a measure of atomic hydrogen (H and D) mobility at various annealing temperatures (from 24 to 30 K). The temperature dependencies of the HKrCl and DKrCl formation rates yield similar to64 and 68 meV for the corresponding activation energies estimating the isotope effect on atomic hydrogen mobility in solid Kr (D slower than H). The difference in mobility of H and D atoms allowed us to demonstrate a reaction between D atoms and HKrCl molecules, and the suggested kinetic model is in good agreement with experiment. In addition, the H/D isotope effects on the solid-state photodissociation of HCl and HKrCl are studied and discussed. (C) 2003 American Institute of Physics.