Both binary cluster cations and anions composed of silver (gold) and sulfur atoms were generated by laser ablating the mixed silver (gold) and sulfur powders. From analyzing the compositions and distributions of the cluster ions, we find that the observed AgnSm^±, especially the larger cluster ions, are in ionic bonding, with Ag2S as structural unit, while the observed AunSm^± cluster ions are mainly covalent, with gold atoms bonding together to form the core of the clusters and sulfur atoms coordinating on the surface of the core. Several "magic number" clusters, such as Ag11S5^+, Ag9S5^-, Au8S14^+, Au5S6^-, etc. have been distinguished from the recorded mass spectra.

Key words: STATISTICAL DISTRIBUTION, LASER, TIME-OFF FLIGHT MASS SPECTROMETRY, SILVER SULFIDE, GOLD TRISULFIDE