The Electronic Structure of Diamondoids: When does a Molecule Become a Nanoparticle?

Methane and diamond are common materials with well-known, but extremely different properties. Fundamental, compelling questions then arise: with sp$^{3}$ bound carbon molecules/clusters, at what sizes do diamond-like properties emerge? Pure, defect-free, perfectly hydrogen-terminated diamondoids, from $\sim $0.5 nm to $\sim $1 nm, bridge the gap between molecules and nanoparticles. Furthermore, experiments in the gas phase eliminate particle-particle interaction and ensure measurement of pure, pristine, and undamaged molecules. X-ray absorption probes the unoccupied electronic states; the carbon K-edge reveals rich electronic structure in the series methane, cyclohexane, adamantane, diamantane, through to hexamantane. Diamondoids show the emergence of a diamond-like band structure. Using x-ray absorption and soft x-ray emission, we will compare our experimental LUMO/conduction band and HOMO/valence band positions with predicted changes in HOMO-LUMO gap from several calculations.