Reactivity and Collisionally Activated Dichlorocarbene Dications studied by Tandem Mass Spectrometry.

The dissociation mechanisms of dichlorocarbene dications following collisional activation have been investigated via tandem mass spectrometric technique and semi-empirical calculations. Three channels appear to be significant: (CCl2)2+->CCl+(X1Sigma+)+Cl+(3P) (channel 1); (CCl2)2+->CCl+(X1Sigma+)+Cl+(1D) (channel 2); (CCl2)2+->(Cl2)+(X2Pig)+C+(2P). The second channel becomes dominant at high internal energy. Production of ground state fragments (channel 1) involves a transition driven by spin-orbit coupling from the (CCl2)2+ X 1Sigma+g state to the (CCl2)2+ a 3Sigma-u state en route to the fragments. The dissociation barrier for the production of the ground state fragments from the ground electronic state of (CCl2)2+ via the spin-orbit-induced transition is equal to 420 kJ/mol. The dissociation pathway that corresponds to channel 3 includes a first isomerization step from the linear (Cl-C-Cl)2+ structure to a bent (Cl-C-Cl)2+ connectivity. The calculated isomerization barrier amounts to 550 kJ/mol. The calculated reverse activation barriers are compatible with the measured kinetic energy released on the fragments.