Neutral and ionic clusters of antimony and bismuth: A comparison of magic numbers

Neutral and singly charged anion or cation clusters of antimony and bismuth are produced by laser vaporization in a pulsed nozzle cluster source. Neutral clusters are photoionized near threshold with a fluorine excimer laser, while ionized clusters are sampled directly from the laser vaporization plasma. All species are mass analyzed with a time-of-flight spectrometer. Abundance patterns in these systems exhibit ‘‘magic numbers’’ that are strikingly charge dependent. Compared at the same charge, corresponding neutral and cation spectra of these metals are quite similar, but significant differences arise in the two anion cluster distributions. Neutral cluster growth in these systems ends abruptly at five atoms while the ionized distributions fall off gradually out to beyond 12–15 atoms. These unique patterns are examined in the context of cluster growth dynamics and suspected cluster stability based on the predictions of simple electron counting models.