Reactivity of 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 techniques and semi-empirical calculations. Three channels appear to be significant: CCl22 +→CCl+(XlΣ+)+Cl+(3P)(channel 1)CCl22 +→CCl+(XlΣ+)+Cl+(lD)(channel 2)CCl22 +→Cl2+(X2Πg)+C+(2P)(channel 3) 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 CCl22 +X˜l∑g+ state to the CCl22 +a¯3∑u+ state en route to the fragments. The dissociation barrier for the production of ground state fragments from the ground electronic state of CCl22+ via the spin—orbit-induced transition is equal to 420 kJ mol−1. The dissociation pathway that corresponds to channel 3 includes a first isomerization step from the linear Cl-C-Cl2+ structure to a bent Cl-Cl-C2+ connectivity. The calculated isomerization barrier amounts to 550 kJ mol−1. The calculated reverse activation barriers are compatible with the measured kinetic energy released on the fragments