Vacuum-Ultraviolet-Induced Fragmentation of Furan Studied by Photon-Induced Fluorescence Spectroscopy

Photodissociation of furan was investigated by photon-induced fluorescence spectroscopy using synchrotron radiation over the photon-energy range of 17–47 eV. Dispersed emission spectra recorded at a higher energy, 62 eV, revealed electronically excited hydrogen atoms, CH(A2Δ, B2Σ−, C2Σ+) radicals, and C2(d3Πg) fragments as the dominant emissive photodissociation products observed under the present experimental conditions. Emission yield dependences of the H(n = 3–6), CH(A2Δ), and C2(d3Πg) channels were measured and parameterized using a phenomenological multi-Gaussian decomposition to characterize broad photon-energy regions contributing to the observed emissions. Appearance energies of the H(n = 3–6) and C2(d3Πg) channels were determined from threshold analyses and compared with estimated dissociation energy limits. The observed threshold shifts and photon energy dependences indicate that the formation of the emitting fragments involves multistep dissociation pathways, likely including ring opening and hydrogen migration processes. Relative fragment emission yields were further examined to probe competition between different emissive dissociation channels. Hydrogen, CH, and C2 emissions exhibit distinct photon energy dependences, indicating that different regions of the excited-state manifold preferentially populate different fragmentation pathways. The present work provides new insight into the formation of electronically excited neutral fragments following vacuum-ultraviolet (VUV) excitation of furan and demonstrates that fragment selective optical emission spectroscopy offers a useful approach for investigating the dissociation of highly excited molecular states in heterocyclic molecules.