For a dication dissociating into two singly charged fragments, the corresponding coincidence island will have a slope of -1 following momentum conservation . The most prominent island on figure comes from coincidence between CH + 3 and C 3 H + 3 , an observation which is in agreement with earlier reported results . The slope of this island is -1 indicating that both these fragments originated from the same C 4 H 2+ 6 dication. Thus by considering the slope of the coincidence islands, the doubly charged precursor dication can be identified. Most of the islands seen in figure have a slope close to -1.