The 193-nm photolysis of S_2 (produced from H_2S_2) and SO-2 in solid argon and the changes introduced by annealing are monitored by using Fourier-transform infrared spectroscopy and laser-induced fluorescence. The results highlight short-range atomic mobility distinguished from global long-range mobility. It is shown that under the 193-nm irradiation a small part of S_2 and SO_2 molecules undergo photodecomposition yielding quasi-isolated pairs where the fragments are in close vicinity to each other. In annealing, the short-range mobility results in recombination of these pairs at rather low temperatures (< 15 K), and this known low-temperature thermoluminescence does not require long-range atomic mobility. Also, recombination of two sulfur atoms can be induced through phonon sideband absorption of the geminate photofragments, which introduces light-induced short-range atomic mobility. The simulations on two sulfur atoms in a static Ar lattice support this scenario, demonstrating that the photofragments can be gently separated by a low potential barrier which favors their recombination in annealing. In particular, this quasistable configuration occurs when the two atoms occupy substitutional sites separated by the lattice parameter of 5.31 A.
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