Potential energy curves for 13 lowest electronic states of S-2 and 6 lowest states of ArS are computed at the MRCI level utilizing the CASSCF orbitals. The electronic structure of S-2 is described by the correlation consistent cc-pVQZ basis set, whereas for ArS the augmented version of this basis is combined with ten electron-core pseudopotential basis set for S and Ar, respectively. Thermal and shock wave induced recombination dynamics of sulfur atoms trapped in Ar lattice are investigated by classical Molecular Dynamics simulations. It is observed that atoms separated by nearest neighbor distance of the lattice do immediately recombine even at 1 K with no thermal activation. While separated by one lattice constant, the S atoms stay stable up to 80 K and no recombination is observed in the classical trajectories. Consequently, the simulation was able to reproduce the experimental S+S glow curve only by lowering the reaction barrier by introducing lattice vacancies in the four atom plane separating the S-S pair. Local 1.1 eV kinetic excitation of a lattice atom next to the trapped S-S pair or artificial shock waves initiated by more distant excitation at 2 eV or more greatly enhanced the probability for recombination. Nonradiative D-1-P-3 relaxation of sulfur provides a mechanism for such phonon emission and is discussed as a potential reason for the observed photoinduced recombination in low temperature Ar matrix.