In contrast to decarboxylation from the ground electronic state, the 1(π,π ⃰ ) 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 20ns photolysis pulse, while the secondary OH radicals formed in ~ 2μs. 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.