The dynamics of dissociation and negative ion formation have been investigated for the hyperthermal energy scattering of state-selected OCS+(X-2 Pi(x),upsilon(1), upsilon(2), upsilon(3)) on Ag(111). Experiments reveal the effect that collision energy and internal energy have on the formation of scattered ionic products. An analysis of the appearance threshold and fragment velocity distribution for each scattered product channel [S-(P-2), O-(P-2), and SO-(X (2) Pi)] suggests that three distinct fragmentation mechanisms compete. Prompt impulsive dissociation of neutralized OCS+(X (2) Pi), followed by electron attachment to the nascent O fragment, is responsible for O-(P-2) emergence. The production of SO-(X (2) Pi) relies on a collisionally activated distortion of OCS, forcing the O and S atoms close together while ejecting the central carbon atom. Finally, a comparison between the scattering of state-selected OCS+(X (2) Pi(x), upsilon(1), upsilon(2), upsilon(3)) and S+(S-4) on Ag(111) provides strong evidence that dissociative neutralization of OCS+(X (2) Pi(x), upsilon(1), upsilon(2), upsilon(3)) leads to S-(P-2) fragments. A discussion of time scales for the various dissociation mechanisms is presented. (C) 1997 American Institute of Physics.