done for a much smaller (54-atom) crystal of the same shape in order to minimize computation time. Figure 5b shows the computation for an ideal cubeoctahedron containing 55 atoms as viewed along (1 10). Finally, Figures 5c and5d show the image simulations for the bcc structure as viewed along (100) and (I 1 I), respectively, which should be compared with the experimental images shown in Figures 3g and3h, respectively. Fig. 5. Computer simulations of various structural types for comparison with the experimental micrographs: a) hcp along (100) containing 54 atoms; b) ccp along (110) containing 55 atoms (ideal cubeoctahedron); c) bcc along (100) containing 59 atoms; d) bcc along (1 1 I) containing 59 atoms.
These observations of the important catalyst ruthenium show that its overall crystal structure, and hence its surface structure, change very rapidly under the influence of the electron beam. Earlier studies of small gold crystals[41 indicated that the local temperature in the vicinity of the illuminated area was probably above 500°C. This constantly changing nature of the metal clusters could well be a quasi-liquid state previously not shown to exist because of the difficulties involved in observing or recording it. Recent results from time-resolved NMR spectroscopy["] could be interpreted to mean that the small metal clusters with li- gands surrounding them altered their structure in solution even at room temperature. These results are of crucial importance for future research on the mechanisms involved in catalytic reactions on metal surfaces.