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 p osition- and time-sensitive multi-particle detector which allows the c oincident measurement of the momenta of correlated fragments. Thereby, a kinematically complete image of the molecular break-up can be deriv ed for each individual event. Of special interest are the ''Coulomb ex plosion'' processes like N-2 --> Np+ + Nq+ or H2O --> H+ + H+ + Oq+. I n these cases the pure Coulomb explosion model - though successful in case of H-2- turns out to be insufficient to explain the measured ener gy and angular spectra. In case of H2O better agreement is achieved wi th ab initio MCSCF calculations of the intermediate H2O(q+2+) parent i on.