The fragmentation dynamics of Ar-HCl following ultraviolet photoexcitation is studied both classically and by an exact wave packet calculation. The focus of the analysis is on the partial fragmentation pathway Ar-HCl + hv --> H + Ar-Cl. The results suggest that there is a competition between two different and simultaneous dissociation mechanisms of hydrogen, namely, direct dissociation and indirect dissociation involving a collision between H and Ar. These two dissociation mechanisms populate different states of partial fragmentation and total fragmentation (into H + Ar + Cl), which interfere upon the H/Ar collision. A global interpretation of the photolysis process based on the interference between the two types of dissociation and consistent with all the quantum results found is proposed. Such an interpretation appears to be general for the UV photolysis of a wide variety of hydrogen-bonded clusters. A means to control the interference mechanism in order to enhance the yield of a specific fragmentation pathway is suggested.