COLLISION-INDUCED DISSOCIATION OF LOW-ENERGY BENZENE IONS

The reaction dynamics of collision-induced dissociation of benzene mol ecular ions at low collision energy has been investigated using a tand em hybrid crossed-beam apparatus. The major primary dissociation react ions forming C4H4+ and C3H3+ have been investigated over the range of center-of-mass collision energies from 4.9 to 17 eV. The energy transf er mechanism is impulsive at all energies; side-scattering is observed at low energy and significant angular scattering occurs at the highes t energy studied. At low collision energy the average translational en doergicity 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 ene rgy reaction mechanism by about 1 eV for both channels. A very broad e nergy deposition function is deduced, with energy transfer ranging fro m 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 ener gy deposition in reactant ions which are highly vibrationally excited prior to collisional activation suggests non-ergodic decomposition pat hways are favored. (C) 1997 Elsevier Science B.V.