PHOTOCHEMICAL CLEAVAGE OF METAL-CARBON NANOCRYSTALS AND THEIR RECONSTRUCTION INTO MET-CARS CLUSTERS

Titanium and zirconium metal-carbon clusters are produced by laser vap orization in a pulsed nozzle source and detected with time-of-flight m ass spectrometry. In addition to the now-familiar ''met-cars'' stoichi ometry (M(8)C(12)), larger magic number clusters are produced with nea r 1:1 metal-carbon ratios. The special stoichiometries observed corres pond to face-centered cubic crystal fragments, with a strong preferenc e for fragments with symmetrical x,y,z dimensions. Mass-selected photo dissociation experiments are used to investigate the structural patter ns and stabilities of these systems. Photodissociation of the larger ' 'nanocrystal'' clusters leads to cleavage along crystal planes, produc ing smaller crystals also having highly symmetric dimensions. Photoexc itation of all these crystallites, in particular the 3 x 3 x 3 species , also leads to surface reconstruction, forming the M(8)C(12) met-cars cluster and/or the M(8)C(13) cluster, the latter of which is assigned to a met-cars cage with an endohedral carbon atom.