| Single-wall carbon nanotubes have been produced by dc arc-discharge vaporization of a graphite anode containing a central core of pure cobalt metal catalyst under inert He atmosphere. Transmission electron micrographs show bundles of {dollar}sim{dollar}1.3 nm diameter carbon nanotubes along with large amounts of impurity carbon including amorphous carbon, partially graphitized nanoparticles, nanoparticles of cobalt and cobalt carbide, and fullerenes are also produced in the process. Nonpolarized inelastic Raman scattering spectra show sharp first order lines at 1566 cm{dollar}sp{lcub}-1{rcub}{dollar} and 1592 cm{dollar}sp{lcub}-1{rcub}{dollar} and second order lines at 2681 cm{dollar}sp{lcub}-1{rcub}{dollar} and 3180 cm{dollar}sp{lcub}-1{rcub}{dollar} which are assigned to carbon nanotubes as well as broad first and second order density of states Raman scattering form disordered carbon. The amorphous carbon background is removed spectroscopically by subtracting the scaled Raman spectrum of soot produced without metal catalyst from the Raman spectrum of soot containing nanotubes. The structure and symmetry properties of general chiral carbon nanotubes is reviewed and the Brillouin zone-folding model is applied to deduce the Raman active normal modes of vibration from the band structure of a two dimensional graphene net. Raman scattering results are analyzed in the context of what is known of {dollar}spsp2{dollar} and {dollar}spsp2{dollar}-like carbons.; The gas phase and vapor phase absorption coefficients, {dollar}Asb{lcub}gas{rcub}(omega) (1.5rm eV le homegale 6.0{dollar} eV), of C{dollar}sb{lcub}60{rcub}{dollar} have been measured in long pathlength, quartz optical cells using a custom built UV-vis spectrometer. By careful measurement of the gas phase concentration, {dollar}Nsb{lcub}gas{rcub}{dollar}, in the gas cell, the absolute value of the complex molecular polarizability, {dollar}alphasb{lcub}M{rcub}=alphasbsp{lcub}1{rcub}{lcub}Lor{rcub}+ialphasb2{dollar} where {dollar}alphasbsp{lcub}1{rcub}{lcub}Lor{rcub}{dollar} is determined by a Lorentz oscillator fit, is determined for isolated C{dollar}sb{lcub}60{rcub}{dollar} molecules. Absolute oscillator strengths determined compare well with theoretical calculations. Knowledge of the absolute magnitude of {dollar}alphasb{lcub}M{rcub}{dollar} is used to determine the {dollar}p-T{dollar} phase diagram in the region of sublimation. The molar enthalpy of sublimation, {dollar}Delta Hsb{lcub}sub{rcub}{dollar} compares well with literature values. The Clausius-Mossotti relation is used to find the complex dielectric function, {dollar}varepsilonsp{lcub}rm CM{rcub}=varepsilonsbsp{lcub}1{rcub}{lcub}rm CM{rcub}+ivarepsilonsbsp{lcub}2{rcub}{lcub}rm CM{rcub}{dollar}, of the ideal molecular C{dollar}sb{lcub}60{rcub}{dollar} solid using {dollar}alphasb{lcub}M{rcub}{dollar} and the known density of solid phase C{dollar}sb{lcub}60{rcub}{dollar}. This is compared to the known dielectric function, {dollar}varepsilonsp{lcub}ellip{rcub}{dollar} of real, solid phase C{dollar}sb{lcub}60{rcub}{dollar} from ellipsometric studies on thin films. Quantitative comparison of integrated oscillator strengths for the real and ideal solids reveal that, upon condensation from a gas to a solid, oscillator strength is shifted from dipole allowed, excitons localized on molecules to charge transfer excitons (CTE) ({dollar}sim{dollar}2.5-2.8 eV) where electron and hole reside on adjacent molecules. Coloumbic attraction between electron and hole is postulated to cause the CTE to decay to a self-trapped exciton which further decays to the C{dollar}sb{lcub}60{rcub}{dollar} dimer and polymer. Thus, a mechanism for photopolymerization has been suggested. |
