Experimental data on the concentration dependence of nonlinear third-order optical susceptibility of fullerene C(60) in benzene solution are analyzed. The deviation of the dependence from a linear behavior is attributed to the fullerene aggregation phenomenon in solution investigated previously. The aggregation shifts the four-photon resonance frequency. It is inferred from a comparison of the size distribution function of fullerene clusters in solution calculated previously based on the drop model of clusters with the experimental chi((3))(C) dependence that fullerene molecules incorporated in clusters do not virtually experience resonant four-photon interaction, so that the nonlinear optical response depends only on isolated molecules C, in the solution studied. The possibility of utilizing the nonlinear optical characteristics of fullerenes in solutions in studies of their aggregation is discussed.

The vapour pressure of pure C-76 and its sublimation enthalpy have been determined by Knudsen cell mass spectrometry in the temperature range 637-911 K. The temperature-pressure equation is Inp(Pa) = (-22 806 +/- 820)/T(K) + (24.52 +/- 1.08). The mean sublimation enthalpy at 764 K is (190 +/- 7) kJ/mol. This value is lower than that, (222 +/- 17) kJ/mol, determined by us previously from a mixture of higher fullerenes,(1) confirming further that the mixture of higher fullerenes is not an ideal solid solution. (C) 1998 John Wiley & Sons, Ltd.

The droplet model of fullerene clusters in solutions is used for analysis of experimental data on the concentration dependence of the third order nonlinear optical susceptibility of fullerene C-60 benzene solution and also for determination of heat of solution of fullerenes versus concentration and temperature. The absorption frequency of fullerene molecules involved into clusters is removed out the four-wave mixing resonance which causes the decrease in a number of fullerene molecules interacting with radiation. Therefore the third order nonlinear optical susceptibility is defined only by separate C-60 molecules which are not involved into clusters. The use of cluster size distribution function of aggregated fullerenes in solutions found earlier provides quite good coincigence between the measured dependencies chi((3))(C) and concentration dependence of separate fullerene molecules. The same function is used for determination of the concentration and temperature dependencies of the heat of solution of aggregated fullerenes. The calculated results shed a light on the reason of apparent contradiction between measured data of various authors.

Phenomena and processes related to the behavior of fullerenes in solutions are reviewed. Data on the solubility of C60 and C70 fullerenes in a large number of solvents at various temperatures are presented as well as on diffusion coefficient of fullerenes in solutions. The relation between the factors controlling the behavior of dissolved fullerenes and the clustering tendency they show is analyzed. This tendency, which sets fullerenes apart from other large molecules, underlies many aspects of fullerene behavior in solutions, such as the recently discovered nonmonotone temperature dependence of fullerene solubility in various solvents, the nonlinear concentration dependence of nonlinear optical susceptibility, the sharp dependence of the color of a fullerene solution on the solution composition (the solvatochromatic effect), the concentration dependence of the heat of solution of fullerenes in organic solvents, etc. Growth mechanisms of fractal clusters in fullerene solutions are analyzed along with similarity laws determining the thermodynamic characteristics of fullerite crystals.

The phenomenon of formation of fractal cluster structures in fullerene solutions discovered in recent experiments is analyzed theoretically. As the basis for analysis the standard fractal cluster growth approach is used. The simplest approximation based on the supposed temporal independence of both fractal cluster dimensionality and attachment probability of two clusters does not provide agreement between the measured and calculated cluster growth data. A satisfactory agreement is attainable in a frame of the Reaction Limited Cluster Aggregation model in the supposition that the attachment probability γ depends on cluster size. The best fitting is obtained for the dependence γ = γ0(r0/R)α, where γ0 = 10−7, α = 2. The possible physical mechanism clarifying such a dependence is considered.

We theoretically analyze processes that occur in a gas-discharge plasma of high-pressure rare gases (up to atm) resulting from pulsed energy deposition of about 10 J/cm(3) within a time of several nanoseconds. Based on the analysis of the experimental data on the drift velocity of electrons and the ionization rate of atoms due to electron impact as functions of the specific voltage of the electric field presented in various papers, we calculate the rate constant for the excitation of resonant atomic states by electron impact. The rate constant for the quenching of these states by electron impact is calculated with the use of the exact quantum-mechanical expression under the assumption of near-threshold energy dependences of cross sections of the relevant inelastic processes. The rate constants of detail reverse processes thus obtained are employed to determine the electron temperature at the initial stage of the excitation pulse. The comparison of the results of calculations with recent experimental data for discharges in argon and krypton indicates an anomalously high contribution of direct ionization to the kinetics of the formation of charged particles. The possibility of applying the discharge of the considered type for pumping pulsed lasers employing rare-gas dimers is discussed.

A review is offered of the current knowledge of carbon nanotubes-particles of cylindrical shape made of one or several concentric graphite layers. Nanotube fabrication techniques are considered and possible nanotube structures analysed. Data on electrical and magnetic properties are presented. Relation between electrical properties and structure (in particular, chirality) is emphasized. Potential applications in nanoelectronics and other active areas of research and technology are discussed.

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C70O has been isolated in ca. 0.5% yield by HPLC separation of the soot extract obtained from a novel arc-discharge reactor for fullerene production, The reactor (DC conditions) can be operated continuously for 24 h, employs a rotating cathode and an anode consisting of continuously-fed strips cut from a carbon sheet, The C-13 NMR spectrum of C70O shows that two isomers (1,2-epoxy[70]fullerene and 5,6-epoxy[70]fullerene) are present in a ratio of ca. 43:57 and all 37 peaks corresponding to each isomer have been identified. These are the first [70]fullerene derivatives in which 5,6-addition is preferred over 1,2-addition, this preference probably deriving from the considerable strain that accompanies bridging with a single atom; the greater curvature across the 1,2-positions compared with the 5,6-positions therefore disfavours the former, Differential polarisabilities of the electrons of the 1,2- and 5,6-bonds, a factor producing a variation in reactivity order according to the attacking reagent (but not considered hitherto in the context of fullerene chemistry) may also be significant, The epoxides are unstable towards EI mass spectrometry, in contrast to epoxides possessing additional addends, and this may reflect the reduced cage strain present in the latter.

Phenomenon of aggregation of fullerenes in solutions determines the main features of their behavior. The general theoretical approach to the description of this phenomenon is developed. The approach is based on the droplet model of clusters consisting of a number of fullerenes molecules. The model taking into account the volumetric and surface energy characteristics of cluster showed itself quite well in the explanation of the extraordinary temperature dependence of fullerene solubility observed earlier. Results of the numerical evaluation of the cluster size distribution function in dependence on temperature and concentration are presented. These data are used for determination of the diffusion and thermal diffusion coefficient of fullerenes in solutions. It is shown that the concentration dependence of the fullerene diffusion coefficient can be used as the basis of a new approach to the problem of fullerene enrichment. The higher fullerenes are usually presented as a low admixture to C-60 and do not form clusters. For this reason they have the higher diffusion coefficient than C-60 and can be partially separated from C-60 through diffusion. The different specific separation schemes are considered.

The results of theoretical and experimental studies addressed to the development of dimer Ar and Kr lasers with discharge excitation are presented. The use of the plasma cathode developed recently provides a spatially uniform discharge in Ar (Kr) at pressure up to 10 bar during 10 ns with power input up to 10 J/ml. The evolution of plasma parameters is analyzed theoretically on the basis of electron swarm data measured earlier. The spectral intensities and power input dependences of pulse duration of dimer emission are analyzed in terms of the possibility of stimulated emission.

The diffusion of fullerenes in solution is studied taking into account the recently established formation of clusters containing numbers of aggregated fullerence molecules. Based on a droplet model of a cluster, the distribution function of fullerence clusters by size is obtained for various concentrations of solution. It is shown that dissolved fullerene is present mainly in the form of clusters at saturation conditions, but the contribution of clusters diminishes as the concentration decreases. Since the diffusion mobility of clusters is much less than that of molecules, it leads to the dependence of an effective diffusion coefficient on concentration, which is computed for the case of fullerence C60. The feasibility of the use of this dependence as a basis for a diffusion method of the separation and enrichment of the fullerene extract with a small addition of higher fullerenes is analyzed. Possible schemes for enrichment are discussed.

The phenomenon of the thermal diffusion of fullerenes in solutions concerned with the fact aggregation of fullerence molecules in clusters in organic solvents discovered recently is studied. The mechanism of this phenomenon based on the temperature dependence of the cluster size distribution function is proposed. The temperature and concentration dependencies of the cluster size distribution function calculated previously are used to calculate the thermal diffusion coefficient of C60 fullerene in toluene solution as a function of temperature and concentration. It is shown that the mechanism spoken of dominates in thermal diffusion at the temperature above the phase transition temperature in solid C60. A contribution of the conventional mechanism of thermal diffusion caused by a considerable difference in fullerene and solvent molecule dimensions is estimated.

Alkali metal fullerene compounds XC(60) and XC(70) (X = Li, Na, K) in toluene solution at room temperature with the fullerene monoanion as the reaction product were synthesized. The ratio of the rate constants for the reaction of joining of the sodium atom to the molecule C-70 and that for C-60 is as large as 2.5, which shows that the C-70 molecule is more reactive than C-60. The reaction product (metal/fullerene approximate to 1/1) was filtered and dried. As products of its slow hydrolysis the pristine fullerene and a water soluble compound have been obtained. This compound is dark-brown colored and has the solubility in water of order 150 g/l. VIS and IR absorption spectra show the presence of the intense bands 3500 cm(-1) belonging to OH group. As it follows from XPS data this compound contains the carbon, sodium and oxygen atoms in the approximate ratio 10/1/3. The presence of fullerenes in this compound is questionable, because the quantity of free fullerenes obtained in the hydrolysis reaction is close to the initial one. The possibility for usage the difference in the reaction rates for fullerenes of different kinds for development of a new procedure for chemical enrichment in solutions is discussed.

The crystal structure of solid fullerite C60 at temperatures exceeding 260 K is the face centered cubic one. The intermolecular interaction in this crystal is short range so each C60 molecule interacts only with the nearest neighbors. Substances having the mentioned features form a class of those with some common properties. Thus the thermodynamic behavior of substances belonging to this class is governed by similarity laws in accordance with which the thermodynamic parameters are dimensionless functions of quantities constructed of the mokecular mass μ, temperature T, well depth in the intermolecular interaction potential D and equilibrium intermolecular distance Ro. One of these similarity laws has been used to process known data related to the pressure vapor temperature dependences for fullerite C60. This permits a refinement of the magnitude D = 0.257 + 0.01 eV known up to now with more uncertainty. This magnitude is used for checking the fulfilment of similarity laws for those fullerite thermodynamic parameters for which experimental data are available. The fulfilment of similarity laws permits an estimation of the critical parameters, melting and boiling temperatures, bulk modulus and also the Debye temperature for fullerite. The obtained data are analyzed in terms of the possibility of the existence of fullerene in the liquid state.

The current state of research on fullerenes-carbon molecules consisting of 60, 70, 76, 84 etc carbon atoms placed on the surface of a sphere or a spheroid-is reviewed. The fullerene structures, methods of their generation, processes in which fullerines participate, and fullerene formation in natural gaseous systems are considered. Properties of nanotubules and methods of their preparation are analysed. Other carbon compounds that resemble fullerenes are considered. The behaviour of fullerenes in solutions is described together with the results of relevant studies. The properties of fullerites-crystals made up of fullerenes-are summarised together with the properties of their compounds.

A thermodynamic approach to the problem of maximum efficiency for a chemical laser is developed. Assuming the laser radiation entropy to be negligibly small in comparison with the entropy of the chemically reacting compounds, thermodynamic limitations for the laser efficiency are obtained. A number of kinds of chemical reactions, each one being a source of laser pumping, are explored. It is shown that the most significant restrictions appear for reactions of a recombination type reducing the number of particles in the laser mixture. Photorecombination lasers are investigated in detail. The maximum efficiency for those lasers is computed over a wide range of parameters of the initial mixture.