In contrast to decarboxylation from the ground electronic state, the (1)(pi, pi(*)) excited 3-butenoic acid dissociates by C-O and C-C bond scissions, producing transient OH and HOCO radicals, respectively. The HOCO further dissociates to OH + CO. Laser-induced fluorescence (LIF) observation of OH showed the primary OH radical formation during 20 ns photolysis pulse, while the secondary OH radicals formed in similar to 2 mus. Doppler spectroscopy showed that 36 kcal mol(-1) relative translational energy released into C-O bond fission fragments. It appears that the dissociation occurs from the excited state potential energy surface. (C) 2002 Elsevier Science B.V. All rights reserved.