More Magic Numbers in Titanium-Carbon Anion Clusters: Can ThisBe Explained by Any Structural Growth Pattern?

Titanium-carbon anion clusters with a mass range up to 1800 amu have been generated in a Smalley-type cluster source involving a target rod composed of titanium and graphite powders, and have been analysed by time-of-flight mass spectrometry. In the lower mass range (up to 1200 amu), our mass spectrum reproduces all the magic numbers, which have been reported previously, i.e., Ti₃C^-₈, Ti₆C^-₁₃, Ti₇C^-₁₃, Ti₉C^-₁₅, Ti₁₃C^-₂₂, and Ti₁₄C^-₂₄, in spite of many differences in experimental conditions. In the higher mass range (1200-1800 amu), we observe new magic numbers at Ti₁₅C^-₂₆, Ti₂₀C^-₃₃/Ti₂₀C^-₃₄ and Ti₂₅C^-₄₂, which cannot be accounted for by the previously proposed structural growth patterns. All the magic and local maximum Ti_xC^-_y peaks have a metal-to-carbon ratio of approximately 1:1.7. The present results suggest a further complexity to the structural growth patterns of the transition metal-carbon mixed cluster systems.