Multiple Ionisation and Fragmentation of Molecules

Abstract

The multiple ionisation and dissociation of molecules, e.g. H₂, N₂, H₂O, CH₄ and C₆₀, by fast ions was studied using a position- and time-sensitive multi-particle detector. The data obtained allow a clear separation of various reaction channels. Of special interest are the ‘Coulomb explosion’ processes like N₂ → N^q+ +Nⁿ⁺ or H₂O → H⁺ + H⁺ +Oⁿ⁺. For these reactions the coincident measurement of the momenta of correlated fragment ion yields a kinematically complete image of the molecular break-up process, and the fragmentation energy as well as angular correlations can be derived for each individual event. In the case of H₂ as target molecule the CE model describes the fragmentation energy rather well, whereas in the case of more complex molecules, e.g. N₂, CO and CH₄, the simple CE model is insufficient to explain the measured energy and angular spectra. Better agreement was achieved with ab initio MCSCF calculations which take into account several molecular states of the fragmenting highly charged molecular ion.