Multiply charged neon cluster ions: critical size and Coulomb explosion

Full text: Multiply charged neon cluster ions are formed upon electron impact ionization of large neutral clusters and analyzed utilizing a two sector field mass spectrometer applying techniques developed recently. The critical size for doubly charged neon cluster ions is determined experimentally with isotopically pure 20Ne to be 287. In spectra of natural neon, the presence of doubly charged clusters can be observed as an increase of the ion yield at the same cluster size confirming the above result. This method allows in addition an approximate estimation of the critical size for triply charged cluster ions. Utilizing a beam deflection method 19 it is possible to observe (for the first time) directly the asymmetric fission of multiply charged neon clusters right after the ionization event. The most abundant low mass fragment ion from this reaction process is the dimer ion. The yield of larger fragment ions decreases exponentially with the fragment size. The kinetic energy of the emitted low mass fragment ions is of the order of 200 meV which is surprisingly low when comparing the results with a simple point charge model taking into account the critical cluster sizes presently determined. (author)