Reactions of gold cluster cations Aun+ (n=1-12) with H2S and H2

The reactions of gold cluster cations Au-n(+) (n=1-12) with H2S and H-2 have been studied using Fourier-transform ion-cyclotron resonance (FT-ICR) mass spectrometry. The cluster cations were produced by laser ablation of a gold rod in He atmosphere, and their reactions were observed at room temperature and low total pressures of 10(-7)-10(-5) Torr. Initial products of the reactions with H2S were mainly AuSH+ for n=2, AunS+ for n=4-8 and 10, and AunSH2+ for n=9, 11, and 12. No reactions of Au+ and Au-3(+) with H2S were observed. Even n cluster cations were more reactive than adjacent odd n clusters. The particularly low reactivity at n=1, 3, 9, and 11 is consistent with the low ionization potential of Au-n and the weak binding energy of Au-n(+)-Au. Further sulfuration reactions of AunS+ proceeded to give AunSm+ and finally stopped at AunSm+xH2+ when H-2 release did not occur. The maximum number of sulfur atoms m+x increased with the cluster size up to n=8, while the sulfuration reaction stopped at early stages for ngreater than or equal to9. In another series of experiments, no reaction of Au-n(+) (n=1-12) with H-2 gas pulses introduced into the FT-ICR cell was observed. To investigate the stability of gold hydride clusters, laser ablation of gold in a H-2/He mixture was performed. The hydride cluster cations AunHm+ were produced for n=1-7, while bare Au-n(+) clusters were the main products for ngreater than or equal to8. There is a distinct border between n=7 and 8, as the structure of Au-n(+) changes from planar for nless than or equal to7 to three-dimensional for ngreater than or equal to8, suggesting the stability of hydride cluster cations with planar gold frameworks. (C) 2003 American Institute of Physics.