Collision-induced dissociation of low energy benzene ions

The reaction dynamics of collision-induced dissociation of benzene molecular ions at low collision energy has been investigated using a tandem hybrid crossed-beam apparatus. The major primary dissociation reactions forming C4H4+ and C3H3+ have been investigated over the range of center-of-mass collision energies from 4.9 to 17 eV. The energy transfer mechanism is impulsive at all energies; side-scattering is observed at low energy and significant angular scattering occurs at the highest energy studied. At low collision energy the average translational endoergicity to form C4H4+ ions is approximately equal to the appearance energy of this ion in the benzene mass spectrum. At 10 eV and higher collision energy the average energy transferred exceeds the lowest energy reaction mechanism by about 1 eV for both channels. A very broad energy deposition function is deduced, with energy transfer ranging from about 1 eV up to 10 eV, with most probable energy transfer of about 6 eV. The very high translational endoergicity and broad range of energy deposition in reactant ions which are highly vibrationally excited prior to collisional activation suggests non-ergodic decomposition pathways are favored. (C) 1997 Elsevier Science B.V.