Energetics of fragmentations of indene dication from photoionization experiments

The formation and fragmentation of the indene dication C 9 H 8 2 + is studied using synchrotron radiation. The double-ionization energy of indene amounts to 21.8 ± 0.1 eV. The appearance energies of the fragments C 9 H 7 2 + and C 9 H 6 2 + are 25.8 ± 0.1 eV and 25.7 ± 0.2 eV, respectively. Although the appearance energies are almost the same, the dicationic fragment C 9 H 6 2 + is formed in a higher yield than C 9 H 7 2 + . It is suggested that the elimination of atomic hydrogen is associated with a considerable energy barrier, whereas the H2 elimination proceeds via very small barrier or is barrier-less process with respect to the reaction endothermicity.