Theoretical Confirmation of the Experimental Raman Spectra of the Diamondoid Molecule: Cyclohexamantane (C$_{26}$H$_{30}$)

Diamondoids (C$_{4n+6}$H$_{4n+12}$) are rigid, cage-like hydrocarbon molecules which are superimposable upon the diamond crystal structure. For n=1, we have the simplest diamondoid, adamantane C$_{10}$H$_{16}$. While most of the diamondoids for n$\leq$3 have been synthesized in the lab, routes for preparing larger diamondoids for n$>$4 have not yet been realized. The diamondoid, cyclohexamantane (C$_{26}$H$_{30}$), has recently been isolated from distilled Gulf Coast petroleum.[1] While its structure has been confirmed through x-ray diffraction, mass spectroscopy, and $^1$H/$^{13}$C NMR spectroscopy, its vibrational Raman spectra has only been identified through an indirect comparison with the experimental Raman spectra for adamantane and diamond. We have used density-functional theory (DFT) to calculate a Raman spectra which is in excellent agreement with the experimental Raman spectra for C$_{26}$H$_{30}$, thus providing direct vibrational proof of its existence.[2] $^1$J. E. P. Dahl {\it et al.}, Angew. Chem. Int. Ed. {\bf 42,} 2040 (2003). $^2$S. L. Richardson, T. Baruah, M. J. Mehl, and M. R. Pederson, accepted for publication in Chem. Phys. Lett.