CF-252-PLASMA DESORPTION MASS-SPECTROMETRY OF GOLD CLUSTERS - FRAGMENTATION PATTERNS IN SMALL CLUSTERS AND DIFFERENCES IN SAMPLE COMPOSITION IN LARGE CLUSTERS

A series of small gold phosphine clusters, including [Au6(PPh3)6](NO3) 2(1), [Au6(PPh3)8](NO3)2 (2), [Au9(PPh3)8]-(NO3)3 (3), [Au11(PPh3)8Cl2 ]Cl (4), [Au13(PPh2Me)8I4]I (5), and [CAu6(PPh3)6](BF4)2 (6), have bee n studied using 252-Cf-plasma desorption mass spectrometry (Cf-252-PDM S). This series of well-characterized clusters was studied to develop an understanding of Cf-252-PDMS as applied to gold clusters and, hence , use Cf-252-PDMS to study much larger gold clusters. The study of sma ll gold clusters indicates that extensive fragmentation occurs. Oligom erization of these clusters, or cluster fragments, is uncommon, and ev en when it occurs it is limited. These results allow us to estimate th e molecular mass of much larger clusters, on the basis of the highest observed fragment ion, and not the centroid of peak distributions as s uggested previously. The study of the large clusters, moderated by our knowledge of the spectra of small clusters, indicates that a large go ld cluster, formulated by Schmid as Au55(PPh3)12Cl6, gives spectra tha t indicate that sample composition varies dependent on a number of fac tors. These factors include the source of the sample, the age of the s ample, and the temperature at which the sample is stored. It is also p ossible that the sample is inhomogenous as prepared; it is probable th at aged samples are inhomogeneous and contain at least three clusters of molecular weight ca. 9500,14 000, and 20 000 mu (mass units).