Photolysis and annealing experiments with HI/Xe and H2O/Xe matrixes are described and analyzed. The experimental results indicate reactions between HXeH molecules and thermally mobilized H atoms. These reactions limit the amounts of HXeH molecules formed during annealing and presumably yield H-2 molecules. A simple kinetic model including reactions of rare-gas molecules with mobile H atoms describes well the experimental observations. (C) 2002 Elsevier Science B.V. All rights reserved.