The photodissociation/recombination reactions of chlorine molecules under 355 nm laser radiation in compressed argon gas were studied by canonical molecular dynamics with the Nose-Hoover thermostat. The thermal relaxation and the final thermalized spatial chlorine atom-pair distribution over the dissociating electronic potential were analyzed and also compared with the predictions of the Langevin equation approach. The geminate recombination probability rate constants and quantum yields for all the bound electronic states of the chlorine molecule were calculated. The recombination in the ground electronic state was also studied by the Smoluchowski equation approach. Comparisons between the results of the molecular dynamics and the Smoluchowski equation approaches suggest that the solutions of the simplest diffusion equation consistently underestimate both the geminate rate constants and the quantum yields. Factors that may affect the recombination rate constants and quantum yields in the Smoluchowski equation approach were evaluated. They include local temperature jump due to initial hot atom thermalization, non-Markovian effect, mean-force potential, Cl-Cl long-range potential, and hydrodynamic interactions. For the Cl-2/Ar system, it was found that a near quantitative agreement could be obtained by just taking the non-Markovian effect into account in the framework of the generalized diffusion equation approach. The contribution of mean-force potential, Cl-Cl long-range potential, and hydrodynamic interactions could account for the remaining mismatch in the short time and medium time domains. The effect of local temperature jump due to initial hot atom thermalization was found to be insignificant.