Spontaneous Decay of Highly-Charged Fullerene Ions C60Z and C58z

Using isotope-resolved, two sector field mass spectrometric techniques we have identified and investigated quantitatively the energetics and kinetics (in particular the kinetic energy release, KER) of the spontaneous decay reactions C_60-2m^z+ → C_60-2m-p(z-1)+ ₊ C_p⁺ with m = 0 or 1, z ranging from 3 to 6 and p = 2 and 4. The obtained KER results are not compatible with the properties expected for a single-step fissioning reaction as described by the liquid drop model. Therefore the present data had to be interpreted by a different fragmentation mechanism. This novel reaction sequence, termed auto charge transfer (ACT) reaction, is initiated by the statistically driven neutral C₂ (or C₄₎ evaporation followed by an electron transfer process from the receding C₂ (or C₄) fragment to the remaining highly-charged fullerene ion thereby leading finally to the two charged reaction products observed in the exit channel of the decay reaction. Moreover, in the case that a C₂⁺ loss from C₆₀z+ is occurring in the first field-free region we have been able to demonstrate that it is possible to observe in the second field-free region a subsequent C₂ evaporation from the C₅₈(z-1)⁺ fragment ion.     

Thermally Activated Decay Processes of Isolated Superhot C60 in Molecular Beams

We have studied thermally activated decay processes of an ensemble of isolated superhot C₆₀ molecules in molecular beams by several different methods. Highly vibrationally excited C₆₀ molecules in effusive or supersonic beams (with average vibrational energy of 10-20 eV) were generated in an all ceramic, two-stage high temperature nozzle source. the decay kinetics due to various decay processes of the initially canonical ensemble was followed by a mass spectrometric methods for a large range of initial temperatures (T_o=1100 - 1950 K). the processes studied are: (1) fragmentation (C₂ emission) of the neutral C₆₀ (2) C₂ emission from the C⁺₆₀ ions (3) black-body like radiative cooling, and (4) delayed electron emission. the experiments described here are: (a) Depletion of the integrated C₆₀ flux. (b) Analysis of C₆₀ time-of-flight distributions. (c) Dependence of electron impact induced ionization/ fragmentation of C₆₀ upon its initial thermal excitation, and (d) Thermal energy dependence of delayed electron emission. It is shown that thermal kinetics models using a single set of independently measured parameters uniquely reproduce all the experimental observations. the models take into account the different cooling processes and their time evolution. We analyze in detail the evolution of the initially canonical vibrational energy distribution during the flight time to the detector as it is gradually being distorted due to evaporative and radiative cooling mechanisms. It is concluded that the correct parameters to be used for describing the thermally activated decay kinetics of superhot C₆₀ are activation energy of E_o = 4.3 - 4.8 eV for the neutral fragmentation channel C₆₀ → C₅₈ + C₂ and E₁=4.0 - 4.3 for the ion fragmentation channel C⁺₆₀→ C⁺₅₈ + C₂, and corresponding pre-exponential factors of A_o = A₁ = 2.5 × 10¹³ sec^-1. the emissivity coefficient for black body like radiation was found to be ε = 4.5 × 10^-5.     

Glycine C60 Adduct and its Rare Earth Complexes

Glycine sodium salt reacts with C₆₀ to give a water soluble derivative 1, acidification of which produces a less soluble product 2. When compound 2 is treated with Ln(CIO₄)₃ (Ln=La, Y) in several different molar ratios, insoluble rare earth complexes: C₆₀ (Gly)_xLn_x/3(OH)_y(H₂O)_z (x=7-8, y=4-6, z=2-6) were obtained. These new compounds have been characterized by IR.TG-DTA and XPS spectra.     

Surface Ionization Mass Spectrometric Studies of the Li/C60 System

We have studied the Li/C₆₀ system by the surface ionization mass spectrometry. We have investigated a possibility of the Li@C₆₀ formation via the collisions between Li⁺and C₆₀^- ions in a plasma state, which was predicted by an ab initio molecular dynamics simulation. The LiC₆₀ complex was unambiguously observed. Our results do not allow direct determination of the LiC₆₀ structure but indicate that Li is inside the C₆₀ cage. We have determined the ionization potential of Li@C₆₀ complex (IP = 5.9 ± 0.1 eV), which agrees well with the calculated value of the IP of Li@C₆₀.     

Raman Spectroscopy of the Charge Transfer Complex (TTF)x C60 Br8

We report Raman studies on powder samples of the charge transfer complex (TTF)_x C₆₀Br₈ at room temperature. The phonons show considerable softening with respect to the frequencies observed in the Raman spectrum of solid C₆₀ Brg. The strongest mode at 1464 cm^-1 in C₆₀Br₈ is red shifted to a doublet with peaks at 1414 and 1421 cm^-1, implying an average phonon softening Δω of -47 cm^-1. A comparison with the phonon softening of the corresponding A_g(2) mode in alkali-doped C₆₀ (Δω ~ - 36 cm^-1 for A₆C₆₀, A = K, Rb or Cs) suggests that 8 electrons are transferred per C₆₀Br₈ molecule in the charge transfer complex. The mode at 503 cm_--1 in C₆₀Br₈ is shifted upwards, similar to that in A₆ C₆₀ compounds.     

Solubility of Fullerenes C60 and C70 in Seven Normal Alcohols and Their Deduced Solubility in Water

The solubilities of C₆₀ and C₇₀ at 25°C in seven normal alcohols obey the relationship InY = a + bX + cX², where Y is solubility and X is the Hildebrand solubility parameter of the solvent. Extrapolation to the solubility parameter of water yields solubilities in water of 1.3'10^-11 (C₆₀) and 1.3'10^-10(C₇₀) ng/ml with an uncertainty of one order of magnitude.     

On the Evaporation of C60 in Vacuum and Inert Gases at Temperatures Between 830 K and 1050 K

The binary diffusion coefficient D_AB of subliming C₆₀ in He, N₂ and Ar gas has been determined at a gas pressure between 5 and 10 kPa. It resulted D_AB/(cm^2/s)=D_o(P_o/P_t(T/T_o)ⁿ as a function of the total pressure P_t of the vapor phase and temperature T. At T_o=273 K and P_o=1.0133×10⁵ P_a, the values D_o = (0.059±0.004) cm²/s, (0.011±0.003) cm²/s, (0.012±0.007) cm²/s, n = 1.77±0.06, 2.02±0.18, 1.77±0.37 were obtained for He, N₂, Ar and (830-1000) K, (800-1020) K, (875-1095) K, respectively. Only 40 wt% of the initial C₆₀ material yielded reliable D_AB where the vapor pressure of C₆₀ followed log₁₀(P/Pa) = -(8976±60)/T/K+(11.05±0.07) for T between 640 and 1055 K.     

Magnetic Properties of Some Fullerene Compounds

Magnetic properties of some fullerene intercalation compounds are detailed. A few examples are presented including properties of 1) Acceptors: MoF₆ From magnetic measurements the existence of positively charged C₆₀ (C₆₀⁺) can be inferred 2) Donnors: Yb_xC₆₀ and Eu₃C₆₀ compounds. Magnetic properties of (Yb_xC₆₀) are dominated by crystal field effects. A high field magnetic transition (17 T at 4 K) occurs in Eu₃C₆₀ associated with a large hysteresis of the magnetization and relaxation effects. This complex magnetic behaviour is attribued to Eu²⁺.     

INHIBITORY EFFECTS OF FULLERENE C60 DERIVATIVES ON ENDOTHELIUM-DERIVED RELAXATION IN RABBIT THORACIC AORTA

Inhibitory effects of newly synthesized fullerene C₆₀ derivatives 1 (C₆₀-bis(N,N-dimethylpyrrolidinium iodide)), 2 (C₆₀-proline-N-acetic acid) and 3 (C₆₀-ethylenediamine-N, N'-diacetic acid) on acetylcholine-induced relaxation in endothelium-intact rabbit thoracic aorta precontracted by phenylephrine (10^-6 M) were studied. Fullerene C₆₀ derivative 1 (3 × 10^-6 M), 2 (10^-5 M) and 3 (10^-5 M) reduced the maximum amplitude of the acetylcholine-induced relaxation without significantly changing the pD₂ values obtained from the concentration - response curves. In the presence of fullerene C₆₀ derivative 1 (10^-5 M) the acetylcholine-induced relaxation was eliminated and an acetylcholine-induced contraction was observed. These results suggest that fullerene C₆₀ derivative 1 strongly inhibits endothelium (nitric oxide)-dependent acetylcholine-induced relaxation in thoracic aorta of rabbit.     

Anomalous elastic properties of RF-sputtered amorphous TeO2+x thin film for temperature-stable SAW device applications

The anomalous elastic properties of TeO_2+x thin films deposited by rf diode sputtering on substrates at room temperature have been studied. The deposited films are amorphous, and IR spectroscopy reveals the formation of Te-O bond. X-ray photoelectron spectroscopy confirms the variation in the stoichiometry of TeO_2+x film from x = 0 to 1 with an increase in the oxygen percentage in processing gas composition. The elastic parameters of the films in comparison to the reported values for TeO_2+x single crystal are found to be low. However, the temperature coefficients of elastic parameters of all deposited films exhibit anomalous behavior showing positive values for TC(C₁₁) in the range (32.0 to 600.0) x 10^-40 C^-1 and TC(C¹¹) = (35.0 to 645.5) x 10^-4degC^-1 against the negative values TC(Cn) = -2.7 x 10^-4degC^-1 and TC(C₁₁) = -0.73 x 10^-4degC^-1 reported for TeO₂ single crystal. The variation in the elastic parameters and their temperature coefficients is correlated with the change in the three-dimensional network of Te-O bonding. The anomalous elastic properties of the TeO_2+x films grown in 100% O₂ are useful for potential application in the design of temperature stable surface acoustic wave devices.     

He Ion Bombardment of C70 Fullerene: An FT-IR and Raman Study

C₇₀ fullerene films deposited on a silicon substrate have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₇₀ have been followed by both FT-IR and Raman spectroscopy. The results have been compared to the behavior of C₆₀ fullerene and discussed in an astrochemical context. The main conclusion is that C₇₀, contrary to C₆₀, does not form oligomers at low radiation dose but it is directly and gradually degraded to amorphous carbon (carbon black).     

Effects of Hexasulfobutylated C60 on the Thalamic Neurons in Neonatal Rat in vitro

The effects of hexasulfobutylated C₆₀ (FC₄S) on membrane potentials and currents were studied by tight-seal, whole-cell recording in thin slices of the neonatal rat thalamus. Silent neuron with resting membrane potentials of around -62.4 ± 0.7 mV was found in whole-cell current clamp recordings. Hexasulfobutylated C₆₀ depolarized the neuron by a concentration dependent manner. It also (1) prolonged the decay time constant of action potential and (2) decreased the threshold of the directly elicited action potentials of the neuron. Hexasulfobutylated C₆₀ did not alter the input resistance of the excitable membrane. In whole-cell voltage clamp studies, depolarizing command pulses from a holding potential of about -70 mV evoked a fast inward current followed by an outward current in the thalamic neurons. Hexasulfobutylated C₆₀ (30 - 100 μM) increased the total inward sodium current of the neuron, while hexasulfobutylated C₆₀ did not alter the outward potassium currents in all voltage steps tested. It was concluded that hexasulfobutylated C₆₀ (1) decreased the threshold of the action potential and (2) prolonged the decay time constant of the directly elicited action potential of the neonatal rat thalamic neurons. The effect may be closely associated with the Na⁺ current in thalamic neurons.     

A Study of Fullerene Preparation Technique

A new homemade are fullerene generator used in this experiment is reported. The comparation of yields of fullerenes (C₆₀/C₇₀ mixture) was studied by different power supplies (AC and DC), different gaps of two graphite rods and different He pressure between 0.4×10⁴- 2.8×10⁴ Pa. In our experiment, the highest yield up to 13% was achieved, when DC discharge was used and the optimum He pressure was near 0.8×10⁴ - 1.6×10⁴ Pa.

The mixed fullerene was analyzed by electron impact masa spectnun (EIMS). The relative amount af C₆₀ to C₇₀ was 4.2 to 1. After column chromatography aeperation with hexane on alumina, 99.9% Cso was obtained. FTIR and ^1aC-NMR epectrum were ueed to characterize the pure C₆₀ samples.     

Addition Reactions of Benzyne, Dienes, Dichlorocarbene, and Oxygen to C60

Benzyne was found to add to C₆₀ in good yield to give C₆₀(C₆H₄)_n (n=1-4). Typical Diels-Alder dienes were also found to add to C₆₀ under thermally mild conditions. Adducts of C₆₀ with 2,3-dimethylbutadiene, cyclopentadiene, hexa-chlorocyclopentadiene, 1,3-diphenylisobenzofuran, and anthracene were obtained. Further reactions of these products such as elimination and autooxidation reactions were investigated. Addition reaction of dichlorocarbene to C₆₀ gave C₆₁Cl₂. Oxidation of C₆₀ with m-chloroperbenzoic acid gave C₆₀O_n(n=1, 2). All of the products were isolated by means of HPLC and characterized by mass spectroscopy.     

He ION BOMBARDMENT OF C60 FULLERENE: AN FT-IR AND RAMAN STUDY

C₆₀ fullerene films have been bombarded with He⁺ ions at 30 keV at room temperature in vacuum. The structural changes undergone by C₆₀ have been followed by both FT-IR and Raman spectroscopy. Raman spectroscopy was the most useful tool for this scope. It has been clearly discovered that at low radiation dose C₆₀ forms oligomers but at higher radiation doses it is converted into an amorphous carbonaceous matter. The implications of these results on the possible survival of C₆₀ fullerene in the interstellar space have been discussed briefly in connection with the previous results on the effects of various types of electromagnetic radiation over C₆₀.     

Arylation of [60]Fullerene with Br2/FeCl3/PhH: Formation of C58 Derivatives via CO Loss

Heating a mixture of [60]fullerene, bromine, ferric chloride and benzene under reflux for 24 h products a range of phenylated [60]fullerene derivatives. The main product is C₆₀Ph₅H but other components identified by mass spectrometry (and in some cases separated by HPLC) are: C_6oPh_n(n = 4, 6, 8, 10, 12), C₆₀Ph_nO₂(n = 4, 6, 8, 10, 12), C₆₀Ph_nOH (n = 7, 9, 11), C₆₀Ph_nH₂ (n = 4, 10), C₆₀Ph₄H₄, C₆₀Ph₅H₃, C₆₀Ph_n0₂H (n = 5, 9), C₆₀Ph₄C₆H₄O₂, C₆₀Ph₉OH₃, and C₆₀Ph₁₁ O₃H₂. In the corresponding reaction with toluene, the crude reaction mixture contained C₆₀(MeC₆H₄)₄ as a main product; C₆₀(ClC₆H₄)₅H was obtained from the reaction with chlorobenzene. Formation of these derivatives is believed to involve radical bromination of the fullerene, followed by electrophilic substitution of the hatogenofullerene into the aromatic, accompanied in some case by hydrolysis, elimination and epoxide formation; oxidation may also introduce ketone/dioxetane functionality. The EI mass spectra of C₆₀Ph₄O₂ and C₆₀Ph₈O₂show degradation to C₅₈Ph_n (n = 0-8), having structures believed to be related to the pseudofollerenes C₆₈Ph_n (n = 0-8) reported recently. These results suggest that some derivatisations of fullerenes confer stability, due to the relief of strain.     

EPR of Graphite and Fullerenes

Analysis of the EPR results for graphite and fullerenes has led to the development of a model for the g-factor in follerene based on the analogy between graphite and fullerene. Pressure dependence of g-factor in C₆₀ powder confirms the validity of this model. ¹³C hyperfine splitting of_a0.36 mT in pristine fullerene is also reported. The g-factors of C₆₀^-1 and C₆₀^-3 in a solution and in a different K°C₆₀ fullerides are presented. C₆₀⁺ⁿ states should be described by the spectroscopic splitting factor larger than that of a free spin.     

Pyrolytic Trifluoromethylation of [76]-, [78]-, [84]-, and Aza[60]Fullerenes with Silver Trifluoroacetate; Evidence for Coordination of Fullerenes to Silver

Pyrolytic trifluoromethylation of [76], [78], [84], and aza[60]fullerenes with silver trifluoroacetate at 300°C results in extensive polyaddition of up to 18, 18, 20 and 20 CF₃ groups, respectively. In contrast to trifluoromethylation of [60]- and [70]fullerenes that give a full range of derivatives ranging upwards from C_n(CF₃)₂, [76]-, [78]-, and [84]-fullerenes only give C_n(CF₃)_6-18 derivatives, largely in the 10-12 CF₃ range; reaction with [76]fullerene is accompanied by formation of C₆₀(CF₃)₆ attributed to cage fragmentation. For aza[60]fullerene the hexa-addition level dominates, in contrast to its other reactions which give predominantly penta-addition products. All the compounds showed peaks at 1256±2 and 1180-1190 cm^-1, due to the CF₃ group, and peaks in this region are shown also by the soluble extract obtained on trifluoromethylation of nanotubes. As in trifluoromethylation of [60]- and [70]-fullerenes, the products obtained initially are involatile, attributed to formation os silver complexes; these are decomposed on subsequent solution in toluene. Mixed isomeric trifluoromethylated C₆₀F₈ derivatives viz. C₆₀F₇CF₃, C₆₀F₆(FG₃)₂, C₆₀F₅(CF₃)₃ and C₆₀F₄(CF₃)₄, and C₆₀F₄CF₃CF₂CF₃ (a C₆₀F₆ derivative) have been isolated from fluorination of [60]fullerene with MnF₃/K₂NilF₆ at 510°C.     

Thermodynamic Properties and Hydrogen Accumulation Ability of Fullerene Hydride C60H36

Thermodynamic properties of fullerene hydride C₆₀H₃₆ in the ideal-gas and crystal states were studied by theoretical methods. Molecular structures and vibration frequencies were calculated for 9 isomers of C₆₀H₃₆ by the density functional theory (DFT) by use of a combination of the B3LYP functional with 6-31G* basis sets. Ideal-gas thermodynamic properties were calculated based on those parameters. Enthalpies of formation of C₆₀H₃₆ isomers in the ideal-gas state were derived from homodesmic reactions involving adamantane, cyclohexane, and C₆₀ fullerene. Using the standard methods of statistical mechanics, heat capacity and derived thermodynamic properties of crystalline C₆₀H₃₆ were calculated at 340-1000 K that extended the range of experimental measurements. With a crystal-gas heat capacity difference, the experimental value of sublimation enthalpy was extrapolated to room temperature as Δ_subH_m^o (298.15 K)=(193±10) kJ · mol^-1. Combining this value with the known experimental enthalpy of formation in the crystalline state, the ideal-gas enthalpy of formation of C₆₀H₃₆ at the synthesized sample isomer composition was obtained: Δ_f H_m^o (298.15 K)=(1206±28) kJ · mol^-1. Equilibrium constants and compositions were calculated for the reactions of hydrogenation of C₆₀ fullerene in different states. It was shown that C₆₀ can act as a hydrogen accumulator.     

Combustion Calorimetric Studies on C60 and C70

Combustion calorimetric studies on C₆₀ and C₇₀ were made using a new micro-bomb combustion calorimeter. Standard enthalpies of formation at 298.15 K were determined to be (2273±15) kJ·mol^-1 and (2375±18) kJ·mol^-1 for C₆₀ and C₇₀, respectively.