Dissociation of excited 3-butenoic acid at 193 nm: observation of two channel OH formation dynamics by laser-induced fluorescence

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 20 ns photolysis pulse, while the secondary OH radicals formed in ∼2 μs. 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.