During experiments aimed at understanding the mechanisms by which long-chain carbon molecules are formed in interstellar space and circumstellar shells1, graphite has been vaporized by laser irradiation, producing a remarkably stable cluster consisting of 60 carbon atoms. Concerning the question of what kind of 60-carbon atom structure might give rise to a superstable species, we suggest a truncated icosahedron, a polygon with 60 vertices and 32 faces, 12 of which are pentagonal and 20 hexagonal. This object is commonly encountered as the football shown in Fig. 1. The C60 molecule which results when a carbon atom is placed at each vertex of this structure has all valences satisfied by two single bonds and one double bond, has many resonance structures, and appears to be aromatic. Before 1985, it was generally accepted that elemental carbon exists in two forms, or allotropes: diamond and graphite. Then, Kroto et al. identified the signature of a new, stable form of carbon that consisted of clusters of 60 atoms. They called this third allotrope of carbon 'buckminsterfullerene', and proposed that it consisted of polyhedral molecules in which the atoms were arrayed at the vertices of a truncated icosahedron. In 1990, the synthesis of large quantities of C60 [see Nature 347, 354–358 (1990)] confirmed this hypothesis.

C 60 : Buckminsterfullerene

A new form of pure, solid carbon has been synthesized consisting of a somewhat disordered hexagonal close packing of soccer-ball-shaped C60 molecules. Infrared spectra and X-ray diffraction studies of the molecular packing confirm that the molecules have the anticipated 'fullerene' structure. Mass spectroscopy shows that the C70 molecule is present at levels of a few per cent. The solid-state and molecular properties of C60 and its possible role in interstellar space can now be studied in detail.

Solid C60: a new form of carbon

The major part of this chapter has already appeared in [1], but because of the length restrictions (in Science), the discussion on why we think this form is given in only brief detail. This chapter goes into more depth to try to answer the questions of why the fullerenes form themselves. This is another example of the very special behavior of carbon. From a chemist’s standpoint, it is carbon’s ability to form multiple bonds that allows it to make these low dimensional forms rather than to produce tetrahedral forms. Carbon can readily accomplish this and it is in the mathematics and physics of the way this universe was put together, that carbon is given this property. One of the consequences of this property is that, if left to its own devices as carbon condenses from the vapor and if the temperature range is just right, above 1000°C, but lower than 1400°C, there is an efficient self-assembly process whose endpoint is C60.

https://science.sciencemag.org/content/sci/273/5274/483.full.pdf

Crystalline Ropes of Metallic Carbon Nanotubes

Nanotubes from Carbon.

and Applications of Fullerenes, Carbon Dots, Nanotubes, Graphene, Nanodiamonds, and Combined Superstructures Vasilios Georgakilas,† Jason A. Perman,‡ Jiri Tucek,‡ and Radek Zboril*,‡ †Material Science Department, University of Patras, 26504 Rio Patras, Greece ‡Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry, Faculty of Science, Palacky University in Olomouc, 17 listopadu 1192/12, 771 46 Olomouc, Czech Republic

Broad family of carbon nanoallotropes: classification, chemistry, and applications of fullerenes, carbon dots, nanotubes, graphene, nanodiamonds, and combined superstructures.

Laser vaporization of a substrate within the throat of a pulsed nozzle is used to generate a supersonic beam of carbon clusters. The neutral cluster beam is probed downstream by UV laser photoionization with time‐of‐flight mass analysis of the resulting photoions. Using graphite as the substrate, carbon clusters Cn for n=1–190 have been produced having a distinctly bimodal cluster size distribution: (i) Both even and odd clusters for Cn, 1≤n≤30; and (ii) only even clusters C2n, 20≤n≤90. The nature of the bimodal distribution, and the intensity alterations in the observed C+n signals are interpreted on the basis of cluster formation and stability arguments. Ionizing laser power dependences taken at several different photon energies are used to roughly bracket the carbon cluster ionization potentials, and, at high laser intensity, to observe the onset of multiphoton fragmentation. By treating the graphite rod with KOH, a greatly altered carbon cluster distribution with mixed carbon/potassium clusters of for...

Production and characterization of supersonic carbon cluster beams

We perform optical emission studies on the species generated by the laser vaporization of graphite into a pulsed helium flow. With short flow channels prior to free‐jet expansion the emission at short downstream distances is dominated atomic carbon lines and three band systems of C2: d 3∏g–a 3∏u (Swan), C 1 ∏g–A 1∏u (Deslandres–d’Azambuja), and D 1∑+u –X 1∑+g (Mulliken). Partially rotationally resolved spectra of the Δv=−1 Swan bands are analyzed using a band contour approach to obtain rotational temperatures and rough vibrational distributions for C2 d 3∏g. The direct emission spectrum from the short‐channel source becomes a weaker, structureless continuum when viewed at long downstream distances. Similar long‐lived continua are induced by a low‐fluence laser at 266, 355, or 532 nm when it crosses the expansion emanating from a source with a long flow channel. We attribute these continua to the incandescence of hot carbon particles, T=2500–4000 K. The continua are fit to a model in which the Planck black...

Optical emission studies of atomic, molecular, and particulate carbon produced from a laser vaporization cluster source

UV laser excited fluorescence spectra of the jet‐cooled copper dimer are reported. Cu2 is produced via laser vaporization of the metal inside the throat of a pulsed, supersonic nozzle. Strong fluorescence is observed upon excitation of 63Cu2 in the range 287–324 nm, corresponding to several v‘=0 bands of the II–X transition recently found in excitation using resonant two‐photon ionization [Smalley et al., J. Chem. Phys. 78, 2866 (1983)]. The II–X emission spectra are characterized by extremely long progressions in the ground state vibration, enabling us to measure G(v) and ΔGv+1/2 values over the range v=0–72. This data has been fit to yield improved vibrational constants for 63Cu2 X 1Σ+g: ωe =266.43±0.59 cm−1, ωexe =1.035±0.030 cm−1, ωeye =+(1.70±0.58)×10−3 cm−1, and ωeze =−(1.78±0.37)×10−5 cm−1. The G(v) data has also been fit to a near‐dissociation expansion which incorporates the correct limiting behavior of G(v), determined by the asymptotic inverse power contribution to the potential. This fit gives...

UV laser excited fluorescence spectroscopy of the jet‐cooled copper dimer

We use dispersed fluorescence (DF) and stimulated emission pumping (SEP) spectroscopies on the B 2A′–X 2A′ system of jet‐cooled HCO to measure the vibrational energies, resonance widths, and relative fluorescence intensities of 73 bound and resonance states supported by the ground‐state potential energy surface. The SEP experiments use both two‐color resonant four‐wave mixing (RFWM‐SEP) and the more conventional technique in which SEP signals are obtained from fluorescence depletion (FD‐SEP). Where applicable, RFWM‐SEP provides superior spectra to those obtained with FD‐SEP, which is susceptible to saturation broadening that can prevent accurate determinations of resonance widths. The observed bound and resonance states span an energy range of 2000–21 000 cm−1 and comprise a wide range of vibrational excitation among the three vibrational modes, including states with 1–12 quanta of excitation in the C–O stretch, 0–5 quanta of bending excitation, and 0–1 quanta of excitation in the C–H stretch. The width...

The unimolecular dissociation of HCO: A spectroscopic study of resonance energies and widths

We use two‐color laser‐induced grating spectroscopy (LIGS) to obtain double‐resonance, absorptionlike spectra of jet‐cooled NO2 below and above the threshold for predissociation at 398 nm. The grating‐laser frequency is tuned through the dissociation threshold while the probe‐laser frequency is fixed to a specific rotational line of an isolated, cold vibronic band well below threshold. The signal beam diffracts off the ground state depletion grating formed when the grating laser excites a transition out of the rotational level selected by the probe laser. The above‐threshold spectra observed for NO2 indicate that, under collision‐free conditions in the free jet, the LIGS spectrum maps the square of the absorption spectrum. We determine predissociation lifetimes from LIGS linewidths and discuss the temporal decay of the induced grating as a function of its orientation with respect to the jet axis. Finally, we consider the effects of phase matching on two‐color LIGS in the forward geometry and derive expres...

Eric A. Rohlfing

Papers

Production and characterization of supersonic carbon cluster beams

Optical emission studies of atomic, molecular, and particulate carbon produced from a laser vaporization cluster source

UV laser excited fluorescence spectroscopy of the jet‐cooled copper dimer

The unimolecular dissociation of HCO: A spectroscopic study of resonance energies and widths

Laser-induced gratings in free jets. I: Spectroscopy of predissociating NO2