Magic numbers and a growth pathway of high-nuclearity titanium carbide clusters

Titanium carbide anionic clusters have been generated and analyzed by time-of-flight mass spectrometry. Our experiments successfully reproduced all the reported magic numbers in the lower mass range (<1200 amu), i.e. Ti3C8−, Ti6C13−, Ti7C13−, Ti9C15−, Ti13C22−, and Ti14C24− [Phys. Rev. Lett. 78 (1997) 2983; J. Am. Chem. Soc. 120 (1998) 6556]. In the higher mass range up to 1800 amu, new magic numbers at Ti15C26−, Ti20C33−/Ti20C34−, and Ti25C42− are found, which cannot be understood by any of the previously proposed structural growth models. A staggered layer-by-layer growth pathway based on Ti5C8 subunits is introduced. Density functional calculations show high stabilities of the constructed structures.