Donald R. Huffman

The infrared and ultraviolet absorption spectra of laboratory-produced carbon dust: evidence for the presence of the C60 molecule

Abstract In carbon smoke samples prepared from vaporized graphite at elevated quenching gas pressures (e.g. > 100 Torr He) new absorption features have been observed in the infrared (the strongest at 1429, 1183, 577, and 528 cm −1 ). Broader features also have been observed in the ultraviolet (the strongest at 340, 270, and 220 nm). By studying 13 C-enriched samples we have shown that the infrared absorptions are produced by large, pure carbon molecules. The evidence supports the idea that the features are produced by the icosahedral C 60 molecule.

Valence and core photoelectron spectroscopy of C60, buckminsterfullerene

Abstract The MgKα X-ray (XPS) and He(I)/He(II) ultraviolet (UPS) photoelectron spectra of several thin films of C 60 (one to three monolayers) prepared by vapor deposition on gold are reported. The core XPS spectrum shows a single narrow carbon 1s ionization at 285.1 eV. The valence UPS spectra show very sharp valence ionization bands, comparable to gas phase spectra, with wide separations between the lowest ionization energy features. The ionizations are consistent with theoretical calculations based on the highly symmetric truncated icosahedral structure. The first vertical ionization energy relative to the vacuum level is estimated to be 7.6 ± 0.2 eV from these solid state measurements.

Experimental determinations of Mueller scattering matrices for nonspherical particles

Measurements have been made to determine all sixteen elements of the Mueller scattering matrix for two types of nonspherical particles. Rounded particles of ammonium sulfate and nearly cubic particles of sodium chloride in the 0.1-1.0-mum size range have been prepared by nebulizing salt water solutions and drying the droplets. Scanning electron micrographs are used to determine size distributions used in Mie calculations of all matrix elements. The expected symmetry of the scattering matrices across the diagonal was confirmed, and the expected eight of the sixteen elements were found to be zero within measurement accuracy. The rounded particles were found accurately to obey Mie theory, while the cubic particles were poorly described by Mie theory for some matrix elements and some angles. Total intensity and linear polarization measurements are presented also for a series of increasing sizes of rounded and cubic particles. A discussion of the effect of nonsphericity on the various matrix elements is given, and applications of these results are given to analysis of particle properties in the laboratory, the clouds of Venus, reflection nebulae, the zodiacal light, and atmospheric particulates.

A new polarization‐modulated light scattering instrument

A new light scattering instrument is described for measuring, as a function of scattering angle, the elements of the matrix describing light scattered from small particle systems. The instrument uses a piezo‐optical birefringence modulator to modulate the polarization state of the incident light beam, and uses lock‐in amplifier detection of the scattered light. The first and second harmonics of the modulation frequency are used with various combinations of filters and orientations to give the separate matrix elements. A treatment of a simple scattering experiment by means of Mueller calculus is carried through to illustrate the interactions of the light with the scattering system and with the various components of the measuring instrument. Evaluation of the instrumental performance is shown through measurements on two systems of monodisperse polystyrene spheres of average radius 550 and 3940 A, compared with Mie calculations. Further measurements on sulfur colloids are presented, and suggestions of the va...

The infrared emission spectrum of gas-phase C60 (buckmisterfullerene)

Abstract The gas-phase infrared spectrum of C 60 has been observed in emission with the National Solar Observatory Fourier transform spectrometer at Kitt Peak. Bands attributable to the C 60 molecule are found at 527.1, 570.3, 1169.1 and 1406.9 cm −1 . Additional emission features are tentatively assigned to C 70 or combination bands of C 60 . A new, strong emission is observed at 1010.2 cm −1 belonging to an unknown molecule. None of these features can be associated with any of the strong emission bands observed so far in astronomical sources.

Interstellar grains The interaction of light with a small-particle system

Abstract Interstellar dust is suggested to be one of the most thoroughly studied of all small-particle systems, whose characteristics have in some ways not been duplicated in our laboratories. The particles are maintained in complete isolation from one another, in ultra-high vacuum and at low temperature, and have been studied spectroscopically from far infra-red to far ultra-violet. Optical properties of the interstellar dust which are surveyed include effects interpreted as due to surface plasmon bands in the ultra-violet, surface phonon bands and other vibrational absorption bands in the infra-red, linear and circular polarization caused by aligned particles, impurity absorption, and defect absorption possibly caused by radiation damage. A discussion of the possible origins for interstellar grains leads to speculation on their relationship to certain meteorites. Absorption and scattering effects from small particles in general are surveyed by way of Mie calculations for a representative insulator, MgO,...

Electrical conductivity studies of undoped solid films of C60/70

Abstract We report the electrical conductivity,σ, and its temperature dependence from 400 to 160 K measured in 1.5 μm thick, sublimed films of C60/70. At room temperature, σ≈ 10−14 (Ωcm)−1. Reversible structure in the temperature dependence, extending from ≈ 300 to 270 K, may reflect reported phase transitions related to orientational order. Assuming solid C60/70 is an intrinsic semiconductor, the high temperature bandgap is about 1.9 eV and the observations are consistent with a transition to a semiconductor, below ≈ 250 K, with a smaller bandgap. Higher carrier mobilities, due to the increased order below the transition, may also play a role.

Extraction and STM Imaging of Spherical Giant Fullerenes

High-temperature, high-pressure extracts of soot produced by the Kr�tschmer-Huffman technique (KH carbon) were characterized by mass spectrometry and imaging with scanning tunneling microscopes (STMs). The mass spectra of these samples are similar to those of ambient-pressure, high-boiling-point solvent extractions, supporting the idea that solvent temperature and possibly pressure are key parameters in extraction of the giant fuilerenes. The STM images show that the giant fullerenes in these samples are roughly spherical in shape and range in diameter from approximately 1 to 2 nanometers, corresponding to fullerenes containing 60 to 330 atoms. No evidence of bucky tubes was found.

Large odd-numbered carbon clusters from fullerene-ozone reactions

The odd-numbered carbon clusters C119, C129, and C139 have been observed in the mass spectra of toluene extracts of fullerene soots and of the products of ozone-fullerene reactions. Specifically, ozone-C60 reactions yield C119, ozone-C70 reactions yield C139, and ozone-(C60/C70) reactions produce C119, C129, and C139. These unexpected species correspond to dimers of C60, C60/C70, and C70, respectively, less one carbon atom, and are stable gas-phase ions with behavior similar to that of fullerenes. The results suggest a new route to functionalization and derivatization of fullerenes through controlled ozone-catalyzed cage-opening reactions.

EPR spectra of C60 anion and cation radicals

Author Institution: Department of Chemistry, The University of Arizona; Department of Physics, The University of Arizona