Vinylidene dissociation following the Auger-electron decay of inner-shell ionized acetylene

The acetylene-vinylidene isomerization and the dissociation of the C2H22+ dication formed in the inner-shell ionization by electron impact have been studied via Auger-electron-ion and Auger-electron-ion-ion coincidence experiments. The occurrence of the isomerization is proved by measuring the production of the CH2+ fragment ion as well as by detecting the C+-CH2+ ion pair in coincidence. The state selectivity of the technique shows that isomerization mainly takes place in the three 1?u-2 lower states of the acetylene dication.