In contrast to the photoexcitation of hydroxyacetone (HA) at 193 nm resulting in an instantaneous dissociation of the Rydberg (1)(n, 3s) state, on photoexcitation at 248 nm the singlet (1)(n, pi*) excited HA molecule first undergoes intersystem crossing (ISC) to the triplet state, followed by a minor dissociation channel to CH3COCH2 and OH radicals. The real time formation of OH, which is probed by laser-induced fluorescence (LIF), shows a rate constant to be greater than or equal to 10(8) s(-1). The initial rotational state distribution of OH (X(2)Pi) is found to be Boltzmann-like, characterized by a single rotational temperature T-rot of 450 +/- 40 K. The average relative translational energy of the photofragments is determined by Doppler spectroscopy to be 8.7 +/- 2.0 kcal mol(-1). The observation of OH with a modest rotational energy, no vibrational energy, and a large amount of translational energy suggests significant exit energy barrier with the dissociating surface. (C) 2002 Published by Elsevier Science B.V.