How molecules and clusters explode

The multiple ionization and fragmentation of small molecules, e.g. N-2 and H2O, by fast H+, He+, Arq+ and Oq+ ions was studied utilizing a position- and time-sensitive multi-particle detector which allows the coincident measurement of the momenta of correlated fragments. Thereby, a kinematically complete image of the molecular break-up can be derived for each individual event. Of special interest are the ''Coulomb explosion'' processes like N-2 --> Np+ + Nq+ or H2O --> H+ + H+ + Oq+. In these cases the pure Coulomb explosion model - though successful in case of H-2- turns out to be insufficient to explain the measured energy and angular spectra. In case of H2O better agreement is achieved with ab initio MCSCF calculations of the intermediate H2O(q+2+) parent ion.