MOLECULAR-DYNAMICS SIMULATIONS OF THE FORMATION PROCESS OF VERY SMALL DOUBLY-CHARGED PARA-DIFLUOROBENZENE CLUSTERS PRODUCED IN A SUPERSONIC EXPANSION

Molecular dynamics simulations have been used to model dissociation and formation processes of doubly charged para-difluorobenzene (PDFB) clusters. ''Anomalously small'' doubly charged PDFBn greater than or equal to 32+ have been observed in a supersonic expansion through multiphoton ionization (Martrenchard, Jouvet, Lardeux-Dedonder and Solgadi) whereas in the case of benzene, clusters involving less than 23 molecules dissociate through Coulomb fission (Hahn, Schriver and Whetten). In the dynamics simulations, another channel has been evidenced for small multiphoton ionized paradifluorobenzene clusters: the evaporation of one neutral molecule. This evaporation process is competitive with Coulomb fission and could be responsible for the formation of small doubly charged PDFBn clusters.