Observation of multiply charged cluster anions upon pulsed UV laser ablation of metal surfaces under high vacuum

Pulsed N-2-laser ablation of various metal targets (M=Au, Pb, Pt, Bi, Sb) i n high vacuum gives rise to series of neutral as well as singly positively and negatively charged clusters. Largest clusters, ranging in size to >100 atoms, were seen for gold and lead targets. For these metals, mass spectral signal-to-noise ratio was sufficient to also observe a series of doubly ne gatively char ed clusters, Pb-x(2-) and Au2- -commencing at threshold sizes of 35 and 29, respectively. In the case of lead, triply negatively charged clusters (Pb-x(3-), x > 76) were also detected. Multianion threshold sizes result from the metastable decay of hot clusters and are associated with a size-dependent transition from evaporation (i.e., neutral atom loss) to el ectron autodetachment for smaller cluster sizes. (Int J Mass Spectrom 206 ( 2001) 63-78) (C) 2001 Elsevier Science B.V.