“…The dicationic states of this molecule, in particular the ground state, have attracted considerable interest. Methods for their investigation include Auger decay [13,14], charge stripping spectroscopy (see the critical review in [15]), double charge transfer [16][17][18], photoelectron-ion-ion coincidence spectroscopy [19], photoelectron-photoelectron coincidence spectroscopy [20], coincidence spectroscopy of Auger electrons and ions [21][22][23], and quantum chemical calculations [15,[23][24][25][26]. The four lowest dicationic states actually possess a potential-energy surface with a local minimum [23], i.e., CH 2+ 4 can be metastable.…”