Photodissociation of 3-mercaptopropionic acid (MPA), in the gas phase, at 193 nm generates OH, as detected by laser-induced fluorescence. Measurements on the nascent OH(v" = 0, J") reveal that it is produced mostly vibrationally cold, with a rotational population distribution characterized by a temperature of 925 75 K. A major portion of the available energy (similar to 30%) is channeled into relative translation of the photofragments, implying the presence of an exit barrier and that dissociation occurs from an excited state of MPA. Both experimental and theoretical results on dissociation of MPA are compared with that of its isomer, thiolactic acid, and almost similar dynamics are observed from the ground electronic states, but different from the excited states. (C) 2007 Elsevier B.V. All rights reserved.