Properties of noble metal cluster ions X pn (X = Cu, Ag, Au; n < 20; p = −1, + 1, + 2) investigated by LMIS technique

Abstract

Mass spectra of X p n cluster ions (with X = Cu, Ag, Au; n < 20; p = − 1, + 1, + 2) obtained in SIMS (secondary ion mass spectrometry) and LMIS (liquid metal ion source) experiments reveal remarkable behaviour. The X − n ions are more intense for odd n (observed in SIMS), the X + n ions are more intense for odd n (observed in SIMS and in LMIS), the X 2 n ions are more intense for even n ( n ⩾ 3, observed in LMIS). In seeded supersonic beams of neutral X n the intensities do not show any alternation. These findings are common to the three metals with small differences in the modulation of the effects. By using a Gutzwiller model (in which dielectronic correlation are taken into account) we calculate the stabilities of these clusters and show that the forementioned effects are due to the variations of this quantity with n: X − n and X + n cluster ions are more stable for odd n, X 2+ n are more stable for even n, X n clusters do not show such an effect.