Group 14(Si, Ge, Sn, and Pb)/P binary cluster ions have been produced by laser ablation, photodissociated by UV laser and detected with a tandem time-of-flight mass spectrometer. As expected on the double periodicities of group 14 elements, Si/P and Ge/P binary cluster ions, whereas Sn/P and Pb/P binary cluster ions, have similar compositions, respectively. The stabilities of these binary phosphide cluster ions depend on their electronic and geometric structures, and the influence of geometric structures on the stabilities is increasing from Si/P cluster ions to Pb/P cluster ions. "Magic numbers" are observed in two types of binary phosphide cluster ions. One type of magic numbered binary cluster ions is isoelectronic to Zintl polyatomic anions (e.g. Pb 5 2Οͺ ) in condensed phases. These binary cluster ions are composed of group 14 metals mainly, containing only one or two phosphorus atoms. The structures and bonding scheme of these binary cluster ions can be predicted by using Wade's electron counting rule. Another type of magic numbered binary cluster ions is isoelectronic either to the neutral group 14 clusters or to the neutral phosphorus clusters, and thus may present similar structures as their neutral analogues. The possible structures and bonding of the magic numbered cluster ions are further investigated with density functional theory Becke-style 3 parameter using the Lee-Yang-Parr correlation functional calculations. (Int J Mass Spectrom 202 (2000) 261-271) Β© 2000 Elsevier Science B.V.