H. Shiromaru

Electronic absorption spectra of the radical anions and cations of fullerenes: C60 and C70

Abstract The electronic absorption spectra of the radical ions in the title are observed in γ-irradiated glassy polyatomic matrices at 77 K. The spectral features of all the radical ions are consistent with the available information in the literature which includes photoelectron and resonance Raman spectra of C60 and C70. In addition, the observed spectra compare favorably with the results of CNDO/S calculations.

Isolation and characterization of the metallofullerene LaC82

Abstract Using two-step liquid chromatographic method, the metallofullerene LaC 82 has been isolated for the first time from the carbon soot. The isolated LaC 82 was well identified as a stable molecule classified to a novel family of fullerene cage molecules. Comparison of the IR absorption spectra between LaC 82 and C 82 empty fullerene suggests an endohedral form for LaC 82 with the same cage structure (C 2 symmetry) previously proposed for C 82 . The presence of electronic absorption in the near-infrared region strongly supports the formation of an open-shell electronic structure for LaC 82 .

ESR and optical studies of the radical anion of C60

Abstract The ESR and the electronic adsorption spectrum of the radical anion of C 60 produced by electrolysis were measured at room temperatures and at 77 K. A singlet ESR spectrum with g =1.999 appeared only at 77 K while the electronic absorption spectrum was observed both at room temperatures and at 77 K. The small value of the g factor was associated with the residual orbital angular momentum. The irregular vibrational structure of the electronic absorption of the radical anion in the frozen matrix band was suggested as being due to the Jahn-Teller distortion.

Optical Second- and Third-Harmonic Generations in C60 Film

Optical second- and third-harmonic generations in C60 film have been studied using a Nd:YAG laser as the fundamental light source. Observed dependences of the generated second- and third-harmonic intensities on the polarization of light and on the angle of incidence are discussed based on the symmetry of the film structure. The relatively large third-order nonlinear response of || χ(3)(-3ω; ω, ω, ω)|| 2×10-10 esu has been observed.

Neutral carbon cluster distribution upon laser vaporization

The mass distribution of neutral carbon clusters generated by a laser vaporization of graphite in He was safely determined by a single photon (10.5 eV) ionization technique. The resulting mass distribution was surprisingly different from those reported in previous articles. It was found that the carbon clusters generated under a moderate laser fluence condition (0.1–1 J/cm2) consists of mostly even-numbered monocyclic rings with the cluster sizes of n=10–18. The formation mechanism of such neutral carbon clusters upon laser irradiation is discussed.The mass distribution of neutral carbon clusters generated by a laser vaporization of graphite in He was safely determined by a single photon (10.5 eV) ionization technique. The resulting mass distribution was surprisingly different from those reported in previous articles. It was found that the carbon clusters generated under a moderate laser fluence condition (0.1–1 J/cm2) consists of mostly even-numbered monocyclic rings with the cluster sizes of n=10–18. The formation mechanism of such neutral carbon clusters upon laser irradiation is discussed.

Synchrotron radiation measurements of appearance potentials for (H2O)2+, (H2O)3+,(H2O)2H+ and (H2O)3H+ in supersonic jets

The appearance potentials for producing the water cluster ions (H2O)2+, )H2O)3+, (H2O)2H+ and (H2O)3H+ have been determined by synchrotron radiation to be 10.87±0.06, 10.92±0.04, 11.18±0.02, and 11.10±0.02 eV, respectively, using water-argon binary mixture in supersonic jet. The result are discussed within the framework of intracluster excess energy dissipation processes.

Structure and superconductivity of single crystalline C60

Abstract We have succeeded in synthesis of C 60 single crsytals with orthorhombic lattice structure contrary to the known cubic form. The structure of the orthorhombic form was confirmed by a four-circle X-ray diffractometer. The intense microwave absorption signal in low magnetic field was detected on the K-doped C 60 single crystals with the onset of superconductivity at Tc = 17.7 K.

A selective isomer growth of fullerenes

Abstract We propose a new fullerene growth model with a novel picture for selective isomer formation of higher fullerenes. The model described supposes that the fullerene intermediates, consisting of a 5- and 6-membered ring network (a cap-like structure), undergo a facile interconversion by a “pentagon migration” transformation. This energy stabilization process dramatically reduces the possible candidates of isomers with fullerene cages. The model also predicts the preferential formation of two specific isomers, D 2 (5)- and D 2d (23)-C 84 with a fraction ratio of 2:1. This conclusion is in contrast to the recent theoretical prediction that the D 2 (22) isomer with a different fullerene cage is more stable than the D 2 (5)-C 84 .

RESONANCE-ENHANCED MULTIPHOTON ELECTRON DETACHMENT SPECTRUM OF C5-

The resonance‐enhanced multiphoton electron detachment spectrum of C5− was measured. The peaks observed at 470–500 nm were assigned to be 1 photon excitation of 2Πu to the 2Πg state. The vibrational structure gives the symmetric stretching frequency of ν2=718±43 cm−1 for the excited state of C5−.

Ultraviolet photoelectron spectroscopy on the linear conformer of negatively charged carbon clusters Cn− (10≤n≤16)

Abstract 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.