Multicollision-induced dissociation of multiply charged gold clusters, Au-n(2+), n=7-35, and Au-n(3+), n=19-35

Multicollision-induced dissociation (MCID) has been applied to gold dusters , Au-n(2+) (n = 7-35) and Au-n(3+) (n = 19-35) stored in a Penning trap. By application of ion cyclotron resonance excitation and pulses of argon coll ision gas, fragmentation yields have been measured as a function of the clu sters' kinetic energy. The corresponding dissociation energies have been de termined by use of the impulsive collision theory and the quantum Rice-Rams perger-Kassel (RRK) model for the energy transfer to internal cluster modes and for delayed dissociation, respectively. As compared to earlier measure ments of singly charged gold dusters the variation of the stability as a fu nction of cluster size is reduced. The doubly charged clusters show an odd- even effect that is reversed with respect to that of singly charged gold cl usters. This is similar to findings by electron impact ionization/dissociat ion and in line with the expectations far simple metal clusters, where the structure and stability is governed by the number of atomic valence electro ns. However, no cluster sizes of particular stability (magic numbers) are o bserved. In general, the dissociation energy of small clusters is smaller t han that of the larger ones because of the influence of the Coulomb force. In contrast to the singly charged gold clusters the odd-even effect of Au-n (2+) disappears at small cluster sizes n < 11; explained as a consequence o f the dominance of trimer fission in that size region. (Int J Mass Spectrom 202 (2000) 47-54) (C) 2000 Elsevier Science B.V.