Paper NS-ThM11
How Size, Shape, and Bond Strain Affect Electronic Structure in sp³ Carbon-Cage Molecules

Thursday, November 3, 2011, 11:20 am, Room 203

Novel nanocarbons such as fullerenes, nanotubes, graphene, and nanodiamond reside at the cutting edge of nanoscience and technology. This paper presents a fundamental study of how size, shape, chemical functionalization, and bond strain affect electronic structure in several benchmark series of chemically pure, novel carbon-cage compounds ranging from diamondoids (a fully sp³ form of nanodiamond) to cubane. Size and shape are studied with the diamondoid series from adamantane to hexamantane, where the observed gap changes are primarily due to evolution in occupied states, as measured with photoelectron spectroscopy (XPS & UPS). Bond strain is studied with dodecahedrane, octahedrane, and cubane, where increasing bond strain leads to two major changes in the near-edge x-ray absorption fine structure (NEXAFS) spectra. First, a broad C-C σ* resonance in the absorption splits into two more narrow and intense resonances with increasing strain. Second, the first manifold of states previously associated with tertiary C-H σ* in the diamondoid series appears to broaden and shift to lower energy. This feature is more than twice as intense in cubane as octadedrane, even though these two molecules have similar stoichiometries (C₁₂H₁₂ vs. C₈H₈). We attribute the additional intensity to π* states, indicating a high degree of p interaction between parallel C-C bonds in the cubane.