Superexcited states in the vacuum-ultraviolet photofragmentation of isoxazole molecules

The photofragmentation of isoxazole molecules producing excited atomic and molecular fragments has been investigated over the energy range 16-50 eV, using photon-induced fluorescence spectroscopy. The following fragments have been identified by their fluorescence: the excited hydrogen atoms H(n), n = 3-7 and the diatomic CH(A2?, B2?-), CN(B2?+) and C2(d3?g) fragments. The diatomic fragments are vibrationally and highly rotationally excited. The fragmentation yield curves for the CH(A2?), CN(B2?+), C2(d3?g) and the H(n), n = 3-7 deduced from their emission yields, were obtained in the photon energy ranges from their appearance energies up to 50 eV. It is found that the fragmentation occurs via excitation into higher lying superexcited states of isoxazole. The vertical excitation energies of these states were determined and their possible fragmentation processes are discussed.