Carbonyl-metal clusters, mass spectra

Similar experiments on a large number of transition metal carbonyls have shown that this process favors dissociation to and detection of metal clusters or atoms. Since most metal-(CO)n photofragments are themselves subject to efficient dissociation, MPI experiments do not identify the primary photoproducts. This situation contrasts sharply with electron impact ionization where the parent ion is usually formed and daughter ions are seen as a result of parent ion fragmentation. Figure 4 shows the electron impact mass spectrum of Mn2(C0) Q (33). for comparison with the MPI mass spectrum of Figure 3. 

The green Mo3 cluster shows three H resonances in the ratio 1 10 5. The peak of area one (58.9, CDC13) is in the range associated with metal formyls (34) and there are two equivalent and one different Cp groups. The carbonyl stretches of the M03 cluster occur at 1763 and 1713 cm-1. The mass spectrum shows a series of Mo3 patterns starting at m/e = 580 with consecutive loss of 5 carbonyls, and a series of strong peaks due to dipositive ions corresponding to the monopositive series 524, 496, 468, and 440. 

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