Search

Flowing gases of hydrocarbon molecules were irradiated by tightly focused ns and fs laser, and the products were captured in hexane solution. In the case of ns laser irradiation, short polyynes up to C 12 H 2 were produced efficiently from all the hydrocarbons, propane, hexane, octane, benzene, and toluene. The yields vary significantly among the products from different target molecules, extending beyond the effects of difference in the vapor pressures. With an aid of the visible emission spectra of the focused spot, polyyne forming reaction is discussed. In the case of fs laser irradiation of hexane, polyynes were produced efficiently much more than the ns-laser case, whereas for the toluene target, polyynes were not produced. Such a variation in the polyyne yield suggests there would be more suitable molecules for formation of polyynes, or any other carbon-rich materials, by gas-phase laser irradiation method.

Soluble fullerenes were produced with a somewhat unexpectedly high yield (10 −2 wt% of the evaporated carbons) by laser ablation of graphite in a ‘room-temperature’ argon gas flow. The high yield was likely due to the high temperature of the graphite after heating by the ablation laser. Laser ablation experiments using argon-diluted propane gas showed that fullerene formation was strongly inhibited by the addition of propane, while the formation of hydrogen-terminated, chain-form carbon molecules (polyynes) was enhanced. The reactivities of the fullerene precursors and chain-form carbon clusters are discussed based on the anticorrelation of the yields of fullerenes and polyynes.

Laser ablation of graphite in argon/propane mixed gases was performed to elucidate the process of carbon cluster growth and hydrogen termination to form polyynes. The carbon-rich materials ejected by ablation were carried by the gas flow and captured by a cooled organic solvent, and then, the soluble products were analyzed by UV absorption. The yield of polyyne increased drastically with the increase of the propane ratios. The propane-ratio-dependent yields for polyynes of various lengths are consistent with a polyyne formation model based on H-abstraction reactions of carbon clusters.

Hydrogen-capped polyynes have been synthesized by femtosecond laser irradiation of hexane liquid. We used UV absorption to identify and high performance liquid chromatography to separate polyynes up to C12H2, and then confirmed with resonance Raman spectroscopy. The shortest hydrogen-terminated chain is found to be C6H2. A supplementary experiment on decane indicates that the formation via single step rearrangement of the parent molecule is not likely.

Single-walled carbon nanotubes made by using arc-burning technique in nitrogen atmosphere were dispersed in sodium cholate (SC) solution, and the diameter and chirality distribution of semiconductive SWNTs was investigated by UV-VIS-NIR and Raman spectroscopy, and photoluminescence mapping technique. In the typical formation condition, the diameter distribution of them is found to be relatively narrow (1.2 nm-1.4 nm in diameter), less chirality dependent, almost the same as the diameter distribution of SWNTs obtained by using laser-furnace technique.

Size-selected linear hydrocarbon molecules, polyynes HC2nH, were contacted in solutions with single-wall carbon nanotubes (SWNTs) prepared from laser-ablated metal/carbon composite rods (Rh/Pt/C) to produce polyyne-encapsulating SWNTs, HC2nH@SWNT(RhPt). New Raman spectral features were observed at 2120, 2061, 2017, 1982, and 1963 cm-1 for five polyynes of n=4–8, respectively, and identified as the vibrational excitation of symmetric stretching modes of the molecules inside the SWNTs. The Raman spectra were compared with those observed for polyynes on Ag islands (SERS) and in solutions. The filling factor was investigated from the concentration dependence of the Raman intensity for HC10H@SWNT(NiCo) to give an estimate of one polyyne molecule per ~350 carbon atoms of SWNTs, providing a picture for head-to-tale filling of aligned C10H2 molecules inside the SWNTs.

We have investigated the electronic structures of single-wall carbon nanotubes (SWCNTs) encapsulating C 70 fallerene and metallofullerenes M(@C 82 (M = La, Gd, Dy), C 70 peapods (C 70 @SWCNT) and metallofullerene peapods (M@C 82 @SWCNT), using photoemission spectroscopy. The photoemission spectra of C 70 and M@C 82 peas are obtained by subtracting the spectrum of pristine SWCNTs from those of the corresponding peapods. The electronic structure of the C 70 peas is similar to that of the C 70 film. For the M@C 52 peapods, on the other hand, the electronic structures of the M@C 82 peas are different. For the La@Cg 82 peapods, the singly occupied molecular orbital (SOMO) for the La@C 82 peas is located nearer to the Fermi level when compared with that in the La@C 82 film. For the Dy@C 82 peapods, the effective Dy valence is estimated to be +2.9. This result demonstrates that effective charges move back from the C 82 cage to Dy fol- ' lowing encapsulation of Dy@,C 82 . peas in the SWCNTs be- ' cause of the strong hybridization interaction between Dy 4f and C 2p electrons, taking into account the Dy valence of +3 in the Dy@C 82 .film.

To study the photoexcitation and subsequent reactions of large molecular ions, anions of 5,10,15,20-tetraphenyl-21H,23H-porphine, which is a typical metal-free porphyrin, were produced and stored in an electrostatic ion storage ring at the Tokyo Metropolitan University. The circulating ions were merged using a pulsed laser, resulting in the production of super-excited anions, which eventually yielded neutral species. The decay profile deviated considerably from t-1 behavior, depending on the laser fluence and excitation wavelength.

A delayed ionisation experiment has been carried out on laser excited C 76 molecules. Ions and electrons are detected in coincidence to distinguish the ionisation of C 76 from that of C 74 molecules created by the dominant process, emission of C 2 . From the power-law dependence of the C 76 + yield on time we deduce the dissociation energy, E d = 8.2 ± 0.3 eV. The relative yield of C 74 + is consistent with very similar Arrhenius parameters for C 76 and C 74 , both for ionisation and for C 2 emission. With the assumption of a frequency factor for dissociation, A d = 10 19 s −1 , the power of photon emission from neutral C 76 is also determined from the experiment. It is consistent with predictions based on oscillator strengths derived from inelastic electron scattering.

We have investigated exciton luminescence spectra, decay behaviors, and their temperature dependence in single-walled carbon nanotubes in micelles. The temperature dependence of luminescence spectra can be explained by the one-phonon process associated with the radial breathing mode in the single-walled carbon nanotube. The luminescence decay behavior suggests that the signal is composed of various exponential decays with different decay times. These experimental results are explained by the existence of trapping centers on the nanotube.

A novel, artificial neural network-based method is now available for obtaining the mean diameter of single wall carbon nanotube (SWCNT) samples from the diameter dispersive features of their Raman G-band. The method is demonstrated here for six different diameter SWCNT samples and 14 different excitation wavelengths. With an adequately large pool of standard nanotube samples, the suggested method is a useful complementary technique for SWCNT diameter analysis as it is capable of rapid diameter evaluation without prior knowledge of the relevant phonon dispersion relations.

We have investigated carrier relaxation dynamics in both metallic and semiconducting single-walled carbon nanotubes by means of femtosecond pump-probe experiments. The femtosecond excitation pulse bleaches the absorption bands of both metallic and semiconducting tubes. In the metallic tubes, the change in the absorption spectra vary from bleaching to broadening. The relaxation aspects of the spectral features change from internal thermalization to electron temperature cooling. In the semiconducting tubes, the nonradiative channel governes the recovery behavior via trapping at defects in the SWNTs.

A 15 keV H+ or 120 keV Ar8+ beam was collided with benzene-d6 to induce multiple ionization and dissociation. The TOFs of the recoil ions were measured combined with the multiple coincidence technique and the position-sensitive measurement, which allow to identify various dissociation channels and to derive their kinetic energy releases (KERs). By qualitative analysis of TOF coincidence map, it is concluded that in the case of high vibrational excitation, doubly charged parent molecule dissociates into two molecular ions with equal number of carbon atoms in each of them. Comparison of coincidence maps obtained by collisions with H+ and Ar8+ indicates that the number of neutral D-substitution, which were missing from dissociation products, can be used as an indicator of vibrational excitation of parent molecule.

By collision of 120 keV Ar8+ with planar hydrocarbons, ethylene and benzene, dissociation of multiply ionized target molecules was studied, focusing attention on the possibility that all the fragment ions are ejected, or tend to be ejected, in a single plane. The trajectories of fragment ions were determined by position-sensitive time-of-flight measurements and the angular correlation of the initial velocity vectors was compared to the results of a reference non-planar molecule, ethane. To eliminate ambiguity due to the contribution of the residual gases, dissociation of ethylene-d4 and benzene-d6 was also examined. The results indicate that the initial velocity direction of the fragments indeed tends to be confined in a single plane when the target molecules are planar. That is, the angular correlation of fragment ions conserves the information on the molecular structure even for considerably large molecules.

Single-wall carbon nanotubes (SWNTs) were synthesized directly on cobalt fine particles by chemical vapor deposition, where nanometer-sized catalyst particles were supplied by pulsed laser vaporization in an ethanol-vapor-flowing quartz tube. Transmission electron microscope observation revealed that the bundle of SWNTs with less amorphous carbon material was obtained using this technique. Dependences of the amount and the diameter distribution of the obtained SWNTs on the furnace temperature were investigated by Raman spectroscopy.

Three isomers of difluorobenzene were multiply ionized by low-energy collisions with Ar8+, and their subsequent dissociation was studied using position-sensitive time-of-flight (TOF) measurements combined with a coincidence technique. The vector correlation of the velocities of the two F+ fragment ions was examined and found to be sensitive to the structure.

We have prepared aligned single-walled carbon nanotubes in polymer by mechanical stretching. The polarized absorption and Raman spectra of the aligned samples have been investigated. The optical transitions in nanotubes strongly depend on the angle θ between the polarization of the incident light and the nanotube axis: the absorbance measured at the peak energy shows a maximum at θ=0°, and they are suppressed at θ=90°. Raman spectra also show strong polarization dependence, which is mainly determined by the dependence of the oscillator strength of optical transitions in nanotubes.

The Raman G-band of six single wall carbon nanotube samples with known diameters between 1.05 and 1.56 nm was measured with 14 different lasers in the 457–676 nm range. Spectra were reduced in size by discrete cosine transformation and introduced as input vectors into a Kohonen self-organizing map (SOM). Even though no diameter data was supplied to the network, the SOM was able to identify spectra belonging to the same sample. The results correlated well with those obtained by conventional cluster analysis. This suggests that artificial neural networks are capable of extracting diameter information from the G-band fine structure.

Single-walled carbon nanotubes (SWNTs) were prepared with double laser vaporization of a graphite target and a metal/alloy target inside an electric furnace at 1200 °C ambient temperature with 500 torr Ar gas atmosphere. Each target was vaporized simultaneously with a different Nd:YAG laser. Several kinds of metal/alloy target (Ni, Co, Fe, and permalloy) were tested in order to see the difference in the resulting SWNT yield and the diameter distribution of them. The Raman spectra of SWNT-containing soot prepared by use of this technique with permalloy/carbon system indicated that permalloy gives almost the same yield as compared with Ni/Co carbon composite rod with single laser vaporization technique, though the diameter distribution of them is slightly different. Also, time-resolved images of the plume by carbon and permalloy nanoparticles after laser vaporization were collected using a high-speed video camera. These images suggest that the hot plumes due to carbon and permalloy nanoparticles do not mix together so extensively, at least in a few hundred microseconds after laser vaporization. The effect of time delay between two laser pulses on the yield and the diameter distribution of SWNTs was also presented and discussed.

To see roles of an ambient gas on the formation process of single-wall carbon nanotubes (SWNTs), we have prepared SWNTs by laser ablation with Ne, Ar, Kr and N2 gases and estimated the abundances of SWNTs mainly by Raman spectroscopy. The abundance of SWNTs was found to depend systematically on the pressure and the molecular mass of the ambient gas, and the highest abundance was obtained in N2 at 1000 Torr. Only N2 produced thinner SWNTs than any other gases, which suggests that the size of nanotube precursors is sensitively affected by the internal freedom of ambient gas.

Single wall carbon nanotubes filled with C60 were analyzed using resonance Raman scattering and electron energy loss spectroscopy. In order to obtain concentrations of the fullerene molecules inside the tubes, the scattering intensity from the fullerenes relative to that from the tubes was used. Since the scattering intensity from the tubes is subject to strong fluctuations, the determination of the concentrations is shown to require averaging of results from different lasers and from all observable Raman lines. The fluctuations are shown to be intrinsic and a consequence of photoselective resonance scattering. Calibration of absolute concentrations can be obtained from electron energy loss spectroscopy performed on the same samples. Samples with three different diameters were analyzed and good agreement between the fullerene concentrations measured by the two methods was obtained.

A multi-hit, position-sensitive, time-of-flight measurement system using a two-dimensional position sensitive detector, which consists of a microchannel plate and a modified-backgammon-weighed-capacitor (MBWC) anode, was constructed for the study of dissociative ionization of highly-charged molecular ions produced in collisions of molecules with highly charged ions. The multi-hit capability of the detector enables event-by-event analysis. With the aid of multi-fold coincidence techniques, studies of the Coulomb explosion of multiply ionized triatomic molecules have been carried out by measuring the velocity components of all three ionic fragments produced in the fragmentation process.

Single-wall carbon nanotubes (SWNTs) encapsulating fullerenes, so-called fullerene peapods, were synthesized in high yield by using diameter-selected nanotubes as pods. Transmission electron microscopy revealed high-density fullerene chains inside the nanotubes. X-ray-diffraction measurements indicate 85% filling for C60 and 72% filling for C70 molecules as a total yield. Interestingly, C60 peas do not show any thermal expansion while C70 peas show normal behavior. Room-temperature Raman spectra show one-dimensional photopolymerization of C60 inside nanotubes by blue-laser irradiation, suggesting molecular rotation inside them. In C70 peapods, no photopolymerization was observed but the relative Raman intensity of each peak is different from the C70 3D crystal. This is probably caused by mixing of two different crystal structures in C70 peas. Furthermore, we synthesized Zn-diphenylporphyrin peapods. Optical absorption and Raman spectra suggest that the encapsulated molecules are deformed by interaction with the SWNT.

Raman spectra have been demonstrated repeatedly to be a very valuable tool for the analysis of new carbon phases such as fullerenes and single wall carbon nanotubes (SWCNTs). Recently it was demonstrated from TEM analysis that C 60 can be encapsulated into SWCNTs. The structures have been given the name ‘peapods’. The concentration of the encapsulated ‘peas’ and the bonding structure in the tube are still unknown but under heavy discussion. From experience with C 60 and SWCNTs, Raman spectroscopy is expected to be a key technique for the analysis of such structures. In our experiments, we found two modes in the region of the pentagonal pinch mode of C 60 . The resonance behavior for these two modes and their temperature dependence is shown in this paper.

Single-walled carbon nanotubes (SWNTs) were grown from the condensed phase by thermally post-annealing of a soot-like material, possibly containing precursors for SWNT growth. The soot-like material was obtained by laser ablation of Ni–Co–graphite composite targets at 550–700 °C. This initial material did not contain any SWNTs but post-annealing treatment inside an electric furnace at 1200 °C under argon flow resulted in SWNTs. The soot-like material prepared at lower temperatures (room temperature to 400 °C did not yield SWNTs even after post-annealing. These results indicate that the precursors for the growth of SWNTs can form only above a certain threshold temperature, about 550 °C. Once these precursors are present, SWNTs can grow by annealing of the metal–carbon mixture. A growth model is proposed based on these results.

Time evolution of emission by carbon nanoparticles generated with a laser furnace technique was investigated with a high-speed video camera. Assuming blackbody radiation formula for small spherical particle, the internal temperature of these carbon nanoparticles was determined as a function of time delay (Δt) after laser vaporization. It was found that the internal temperature of them drastically decreased at Δt 400μs. This finding suggests that a certain exothermic process related to the formation of C60 and other higher fullerenes should occur at Δt > 400μs inside the furnace.

We report on the evaluation of the distribution of diameters for nanotube samples with a wide variation of mean diameters. Such results were obtained from a detailed analysis of the radial breathing mode Raman response and compared to results obtained from an evaluation of optical spectra and X-ray diffraction pattern. The evaluation of the Raman data needs a well refined analysis as the experimental analysis exhibits a rather complicated and oscillating relation between response and exciting laser. Both, an exact calculation where the density of states was considered explicitly and an approximate calculation were applied. Both models used for the analysis are able to explain several unexpected results from the experiment such as the oscillating behavior of the spectral moments, unusual discontinuities in the first moments of the Raman response for excitation in the IR, a fine structure for the response in optics and Raman, and an up shift of the RBM frequency as compared to qualified ab initio calculations. In detail the first moment and the variance of the spectra were used for the evaluation of the diameter distribution. To obtain good results between experimental and theoretical oscillation pattern the transition energy between the first two van Hove singularities had to be scaled up which is considered as a result from coulomb interaction of the electrons in the tubular material. On the other hand the analysis does not only allow to determine the mean value and the width of the diameter distribution but yields also a value for the average bundle diameters or, alternatively, the strength of the tube-tube interaction. The model used for the analysis of the Raman data is also appropriate to analyze the optical response, at least for the spectral range from 0.5 eV to 3.5 eV. The fine structure in the response for the transitions between the three lowest van Hove singularities is well reproduced and the mean tube diameters and their distribution is obtained in very good agreement with the results from the Raman analysis. From the X-ray analysis the same mean values and comparable distributions for the tube diameters were received whereas the bundle diameters could not be retained with high precision in this case.

Encapsulated and hollow closed-cage onion-like structures of WS2 and MoS2 were prepared by laser ablation of the corresponding layered structures in argon atmosphere at four varied temperatures. A detailed study for WS2 indicates that only metal-filled onion-like structures are produced at temperatures Tless-than-or-equals, slant650°C, whereas a mixture of metal-filled and hollow structures are produced at Tgreater-or-equal, slanted850°C. The encapsulated metal is identified to be predominantly the metastable β phase of tungsten. Very short tube-like or elongated polyhedral structures are also obtained at high temperatures.

Adsorption properties of nitrogen and oxygen gases in single-walled carbon nanotube (SWNT) bundles were investigated by the isotherm and X-ray diffraction (XRD) studies. In the as-grown (AG) nanotubes with close-ended caps, both the gases are adsorbed only in the interstitial channels between triangular packed nanotubes. In the heat-treated (HT) nanotubes with open ends, the gases are adsorbed first in the inside of tubes, and next in the interstitial channels. In each site, gases can be adsorbed with the stoichiometory of C 20 N 2 or C 20 O 2 as a monolayer. These results indicate that the inside of nanotube has strong affinity for gas adsorption than the interstitial channels of bundles.

Explosive fragmentation of highly charged CS2q+ ions formed by low energy collision between Ar6,8+ and an effusive molecular beam of CS2 was studied using triple coincidence measurements of the fragment ions combined with a position-sensitive time-of-flight (TOF) detector technique. Detailed analysis of the 3-dimensional velocity vectors of the fragment ions resulting from multiple ionization predicts a reconstructed bond angle that is reasonably consistent with the known structure of the neutral CS2 molecule.

Single-wall carbon nanotubes (SWNTs) were synthesized by laser ablation of Ni–Co-graphite composite targets at 1200°C under argon gas. The effects of the temperature gradient near the target and the gas flow rate on the diameter distribution of SWNTs were studied in order to understand their growth dynamics. Raman spectroscopy was used to analyze the diameter distribution of SWNTs. The flow rate was found to affect the relative yields of SWNTs having different diameters when the temperature gradient around the target was large. Scattering images from the ablated species at different flow rates, recorded by a high-speed video camera, indicated that 10 ms after the ablation the velocities of backward moving species increased with increasing flow rate. These findings are used to estimate the time required for determining the diameter distribution and the growth of SWNTs.

We have separately probed the doping behavior of semiconducting and metallic single wall carbon nanotube (SWNT) films, by optical absorption and dc resistance measurements. Either electron acceptors (Br 2 , I 2 ) or donors (K, Cs) were used as dopants with controlled stoichiometry. Disappearance of the absorption bands at 0.7, 1.2 (assigned to semiconducting SWNT) and 1.8 eV (assigned to metallic SWNT) and the concomitant decrease of resistance due to doping were attributed to electron depletion or filling in specific bands of semiconducting or metallic SWNT. This demonstrates the amphoteric doping behavior of SWNT. Semiconducting and metallic SWNT undergo charge transfer in a specific sequence: initially the transition at 0.7 eV, subsequently around 1.2 eV and finally the feature at 1.8 eV are affected depending on the concentration of the dopant. Changes in the electronic properties are discussed in terms of charge transfer mechanisms in the framework of the rigid-band model.

Multiwalled carbon nanotubes (MWNTs) with high quality were prepared by DC arc discharge of pure graphite electrodes in hydrogen gas. Because these MWNTs co-existed with few carbon nanoparticles compared with the usual MWNTs prepared in helium gas, their purification could also easily be done by infrared irradiation in air at 500°C for 30 min. Resonance Raman spectra of purified MWNTs were measured, and breathing modes at about 500 cm −1 corresponding to a very thin central hole of about 5 A diameter were found. A new peak at about 1840 cm −1 appeared for pristine MWNTs, and its intensity strongly depended on the preparation conditions (pressure of hydrogen gas). The measurement of temperature dependence for electric resistance of MWNTs showed metallic or semiconducting tendency. Purified MWNTs could be used as bright and long-life field emitters for cathode ray tubes, and a desirable current density of 1 mA/cm 2 could be stably achieved at a field of 1.2 V/μm.

Laser ablation of a graphite rod and in situ separation of carbon soot by a temperature-gradient sublimation was systematically investigated using a laser-furnace apparatus. LD-TOF (laser desorption time-of-flight) mass spectra for the carbon deposits after separation show characteristic features of mass distributions mostly caused by the differences in size and structure. It was also found that some portions of the carbon deposits were strongly influenced by the experimental conditions such as the ambient temperature of an electric furnace. Laser Raman spectroscopy was also applied to deduce structural information of the carbon deposits. Furthermore, in order to characterize the laser ablation processes under exactly the same condition used for generating a high yield of fullerenes, we performed emission spectroscopic experiments by use of a high-speed video camera under several different conditions. Based on these experimental findings, the formation processes of carbon nanoparticles including fullerenes are discussed.

Laser furnace technique has been used for diameter selective formation of single-walled carbon nanotubes (SWNTs) using NiCo, RhPt and RhPd catalysts. Particularly RhPd catalyst can produce very thin SWNTs in high yield. In this work, we investigated the furnace temperature dependence for each catalyst to control the diameter of SWNTs more strictly. Further, we investigated the effect of the gas flow velocity to see the growth time of SWNTs. When the flow velocity was changed from 1.2 to 12 mm/s, the diameter distributions of the SWNTs obtained were changed significantly. This result suggests that the nucleation and the growth of SWNTs are much slower than the fullerene formation. Using the slow growth nature of SWNTs, there is a possibility of further diameter control of SWNTs.

The photoelectron spectra of C60 - produced with three different generation methods were recorded with 6.4 eV photon energy using a magnetic-bottle-type time-of-flight photoelectron spectrometer. From these spectra, it was suggested that the laser vaporization of a graphite rod mainly produces C60 - of ring-like structure. On the other hand, C60 - produced by the fragmentation process of the fullerene C70 through C2 or C 2n elimination give different photoelectron features from those of C60 - having an icosahedral (Ih) symmetry or a ring-like structure.

In order to elucidate the formation processes of empty and endohedral fullerenes, we produced fullerenes and endohedral fullerenes by changing La concentration as well as furnace temperature. The yields of these products were systematically investigated by ultraviolet-visible (UV-VIS) absorption spectroscopy and electron spin resonance (ESR) and high-performance liquid chromotography (HPLC) analyses. As a result, it was found that the C60 yield decreases monotonically when La concentration increases, while the LaC82 yield shows a maximum at 0.25 atom %, and then decreases monotonically by increasing La concentration as like as C60. From the HPLC analysis it was also found that the yield of higher fullerenes decreases more rapidly because of the presence of La.

The ambient temperature dependence of the yield of fullerenes was systematically investigated toward furthering the understanding of the fullerene formation mechanism. The change in yield of fullerenes from C60 to C96 was quantitatively examined as a function of fullerene size, temperature, and position of target in the gradient of temperature. As a result, it was found that the formation of higher fullerenes requires higher furnace temperature, presumably because of the presence of higher reaction barriers prior to the accomplishment of the fullerene cage. In connection with such a thermal effect on the yield of fullerenes, we have also carried out an experiment to deduce the spatial distribution of such an endothermic reaction area in which the external heating is effectively active. Furthermore, in order to establish the presence of such a particular area for the fullerene formation, we used a high-speed video camera to directly detect emission from hot particles, which was found to be closely related to fullerene formation.

13 C-NMR studies of new class of C 60 superconductors, (NH 3 ) x Na A 2 C 60 with A=K or Rb, are reported. The results are compared with the other classes of A 3 C 60 superconductors. In fee A 3 C 60 , an examination of the modified Korringa relation, T 1 TK 2 ∼ βS showed existence of weak but substantial antiferromagnetic spin fluctuation in A 3 C 60 ; β =0.40~0.58 with an error of ±20 %. Stoner enhancement factor was also determined as 1∼1.5. The temperature dependent T 1 TK 2 , which becomes significant at high temperature (>∼100 K), is suggested to be explained by an enhancement effect related to short mean free path in the present materials. In (NH 3 ) x Na A 2 C 60 , a gap-like behavior in temperature dependence of 13 C-spin lattice relaxation rate was observed. C 60 and NH 3 molecular dynamics are also discussed.

The Coulomb explosion of ${\mathrm{CO}}_{2}$ in collisions with ${\mathrm{Ar}}^{8+}$ ions of 120 keV has been examined experimentally using a position sensitive detector with a triple coincidence technique. The technique has allowed the full characterization of the structure of the exploding molecule. Purely Coulombic fragment energies fit the experimental results well, across the range of fragment energies. Modifications to the molecular geometry are observed, in the form of widening of the zero point bend distribution and sequential processes are found to be unimportant in the dissociation process.

Four kinds of single-wall carbon nanotubes (SWNTs) with different diameter distribution have been synthesized and optical absorption spectra have been measured. Three large absorption bands due to the optical transitions between spike-like density of states, characteristics of SWNTs, were observed from infrared to visible region. Comparing with the calculated energy band, it has been concluded that the first and the second lowest absorption bands are due to the optical transitions between spikes in semiconductor phases and the third one is due to that in metallic phases. Absorption Peaks sensitively shifted to higher energy side with decreasing tube diameters as the band calculation predicted. Resonance Raman spectra were also measured using various laser lines. When the excitation is in an energy region corresponding to the absorption band of metallic phase, spectra have shown Breit-Wigner-Fano line shape, which is a sign of metallic phase. Using these results, we can easily characterize SWNTs from the optical absorption spectra without Raman measurements and transmission electron microscope observations.

Time-differential perturbed angular correlation method was applied to Ce@C82 in order to investigate the electronic properties of the encaged Ce atom. The nuclear quadrupole frequency of the nuclear spin of the Ce was successfully determined as ωQ = 6.5(3)·107 rad/s, which is much greater than what has already been estimated for Ce4+ and La3+ in other compounds. By comparing the present value with the values for the Ce4+ and La3+, it was inferred that the valence state of the encaged Ce atom is trivalent.

The static spin susceptibility, ${\ensuremath{\chi}}_{s}^{\mathrm{SQ}}$ and ${\ensuremath{\chi}}_{s}^{\mathrm{NMR}},$ in ${\mathrm{C}}_{60}$ superconductors ${\mathrm{K}}_{3}{\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}{\mathrm{C}}_{60}$ was studied using a dc superconducting quantum interference device magnetometer and ${}^{13}\mathrm{C}$ NMR. We found that ${\ensuremath{\chi}}_{s}^{\mathrm{SQ}}$ has a peculiar temperature (T) dependence behaving as $(1\ensuremath{-}{\mathrm{CT}}^{2})$ with a positive constant $C\ensuremath{\sim}(1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}) {\mathrm{deg}}^{\ensuremath{-}2},$ contrary to the almost T independent ${\ensuremath{\chi}}_{s}^{\mathrm{NMR}}.$ These observations indicate a possibility that there exist Kondo-like impurities, whose Kondo temperature is $\ensuremath{\sim}500 \mathrm{K}$ and whose content is $\ensuremath{\sim}0.001$ spins per carbon. On the basis of these studies, the lattice constant dependence of the intrinsic spin susceptibility was established to be $d{\ensuremath{\chi}}_{s}{/da}_{0}=(5.7\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4} {\mathrm{e}\mathrm{m}\mathrm{u}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{C}}_{60}/\mathrm{\AA{}}$ in ${A}_{3}{\mathrm{C}}_{60}$ superconductors where A is an alkali metal.

A C-NMR anisotropic hyperfine coupling tensor was determined as 2p(21.68, 21.68, 3.37) 310 rad/sec for C60 32 in A3C60 superconductors, where A is an alkali metal, by analyzing C-NMR spectra below 85 K. Combined with an isotropic coupling constant of (2p30.69)310 rad/sec, the 2s and 2p characters of the electronic wave functions at the Fermi level were deduced. The results were compatible with local-density-approximation band calculations. From a simulation of C-NMR spectra at superconducting state, the traceless chemical ~orbital! shift tensor and isotropic chemical shift were determined as ~67, 34, 2101! ppm and ;150 ppm, respectively. An estimated magnetic penetration depth is larger than 570 nm in K3C60. Furthermore, the modified Korringa relation, T1TK ;bS ~with Knight shift K, spin-lattice relaxation time T1 , and Korringa constant S!, clearly showed the existence of weak but substantial antiferromagnetic spin fluctuation in A3C60; b50.40– 0.58 with an error of 620%. The Stoner enhancement factor was also determined as 1–1.5 from a comparison between spin susceptibility obtained from NMR and band-calculation results. @S0163-1829~98!00542-6#

Time-resolved difference absorption spectra of polycrystalline thin films of C 60 were measured by femtosecond pump–probe spectroscopy. The decay dynamics of the excited state can be explained in terms of a model of localized excitations. Self-trapped excitons (STEs) are formed after photoexcitation and then converted to polarons. The polarons mainly recombine when they encounter each other after intersite hopping. The decay times of the STEs and polarons are estimated to be 570±120 fs and 54±7 ps, respectively.

Dynamic motion of $\mathrm{Ce}{\mathrm{C}}_{82}$ in the forms of powder and $o$-dichlorobenzene solution is discussed based on time-differential perturbed angular correlation measurements. The observed angular correlations show the presence of two different chemical species of $\mathrm{Ce}{\mathrm{C}}_{82}$. The temperature dependence of the reorientational correlation time abruptly changes at specific temperatures, implying the freezing of the molecular rotation. The data at low temperatures reveal that Ce stays at a certain site for one of the species, whereas for the other the atom has an intramolecular dynamic motion.

A photoelectron spectroscopy technique was successfully applied to the detection and characterization of a linear conformer of negatively-charged carbon clusters from C10− to C16−. By controlling the laser fluence for vaporization it was found that the fraction of a linear conformer was enriched. The presence of the linear form up to C16− was confirmed by the photoelectron spectroscopic evidences. On the basis of the present observations, it was also found that the observed vertical electron affinity up to C16 shows a distinct even–odd alternation, converging into the asymptotic value of ca. 5.0 eV.

HPLC behaviors of metallofullerenes of 14 lanthanoid elements were studied by use of radiotracers, and the species of some of the metallofullerenes were identified by mass spectroscopy. From the HPLC elution behaviors, 14 lanthanoid elements forming metallofullerenes were found to be grouped into two, namely, Sm, Eu, Tm and Yb as one group and the rest of the elements as another. Some new species of metallofullerenes like La@C74, and M@Cn (M=Eu, Tm, Yb; n=74, 82, 84, 88, 90, 92, 94) have been identified. The observed retention times of metallofullerenes are discussed in terms of the number of carbon atoms of the cage and from consideration of the electron donor and acceptor relation between the fullerene species and the HPLC stationary phases.