The mobility of oxygen atoms generated from ultraviolet (UV) photolysis of O-3 isolated in argon matrices is investigated both theoretically and experimentally. The simulations via molecular dynamics show that O(D-1) atoms generated in single, double, and triple substitutional sites can migrate through the matrices by a distance about 1 nm within several picoseconds, but the photogenerated O(P-3) atoms are confined to the original trapping sites. In order to examine the mobility of the O(D-1) atoms experimentally, the probing molecules of CF3Br (or CF3I) are so highly diluted in the matrix of O-3/Ar that the separations between the probing molecules and the precursor ozone molecules are sufficiently large, and the reaction products CF3OBr (or CF3OI) are observed after irradiation with a 266 nm laser. Based on an analysis of the reaction rates, it is shown that the products are only generated from the probing molecules reacting with the O(D-1) but not O(P-3) atoms, suggesting that matrices can serve as a "sieve" for selecting quantum states in chemical reactions.