Tatsuhisa Kato

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.

A theoretical approach to C82 and LaC82

Abstract In view of the recent experimental interest, the relative stabilities of the C 82 isomers and the electronic properties of LaC 82 are investigated by means of molecular orbital calculations. It is calculated that the most stable C 82 isomer has C 2 symmetry, as detected most abundantly via NMR measurement. An interesting finding is that the electronic structure of LaC 82 depends strongly on the position of the La atom. At the energetically most favorable position the electronic state is described as La 3+ C 3− 82 , as suggested from the EPR measurement. It is predicted that the La atom is trapped inside the cage of C 2 symmetry and is strongly bound to the cage carbons; LaC 82 has strong electron-donating character.

ESR studies on cation‐radicals of simple olefins and dienes produced in γ‐irradiated frozen solutions of trichlorofluoromethane

Cation radicals of butene‐1, trans and cis butene‐2, isobutene, tetramethylethylene, cyclopentene, cyclohexene, butadiene, 1,3‐pentadiene, cyclopentadiene, 1,3‐ and 1,4‐cyclohexadienes have been produced mostly for the first time in γ‐irradiated frozen matrix of trichlorofluoromethane at 77 K. Well resolved ESR spectra at 77 K or at 130–155 K permit the determination of proton hyperfine coupling constants. Large hyperfine coupling constants of methylene and methyl protons adjacent to π electron systems indicate an extensive hyperconjugation in the cations. The following photoisomerizations are found: butene‐1+→butene‐2+, cyclopentene+→1,3‐pentadiene+, 1,4‐cyclohexadiene+→ 1,3‐cyclohexadiene+, 1,3‐cyclohexadiene+→1,3,5‐hexatriene+. The nonplanar cations of cyclopentene and 1,3‐cyclohexadiene undergo puckering motion in a limitedly warmed matrix. In the warmed matrix, where diffusions of the cation radicals toward unreacted hydrocarbon molecules proceed slowly, proton transfer reactions are induced. Decisiv...

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.

Spin Crossover by Encapsulation

Encapsulation by synthetic hosts can transform the spin states of square planar Ni(II)(acen) and Co(II)(tap) complexes. Upon encapsulation, the red Ni(II) diamagnetic state was converted into a green paramagnetic state, whereas the Co(II) low spin (S = 1/2) state was changed into a coupled (S = 1/2 and S = 3/2) state. The host cages are noninnocent and host-guest interactions within the confined cavity influence the resultant properties of the enclathrated metal complexes.

Spectroscopic studies of the radical anion of C60. Detection of the fluorenscence and reinvestigation of the ESR spectrum

Abstract An emission band with a mirror image pattern to the near-IR absorption band is detected for C − 60 produced electrolytically in a solution at room temperatures. The emission band reinforces our previous assignment of the absorption band. The lineshape of the ESR spectrum was reinvestigated to conclude that the isotropic feature at temparatures above 50 K is mainly due to the averaging of the Jahn—Teller distorted structures by pseudo-rotation. The significance of the residual orbital angular momentum is discussed.

Does Gd@C82 have an anomalous endohedral structure? Synthesis and single crystal X-ray structure of the carbene adduct.

We report here the results on single crystal X-ray crystallographic analysis of the Gd@C82 carbene adduct (Gd@C82(Ad), Ad = adamantylidene). The Gd atom in Gd@C82(Ad) is located at an off-centered position near a hexagonal ring in the C2v-C82 cage, as found for M@C82 (M = Sc and La) and La@C82(Ad). Theoretical calculation also confirms the position of the Gd atom in the X-ray crystal structure.

State selected ion–molecule reactions by a TESICO technique. IV. Relative importance of the two spin‐orbit states of Ar+ in the charge transfer reactions with N2 and CO

Charge transfer reactions Ar+ (2PJ)+N2→N+2+Ar (1) and Ar+(2PJ)+CO→CO++Ar (2) have been studied for the two spin‐orbit states (J = 3/2 and 1/2) separately using the threshold electron‐secondary ion coincidence (TESICO) technique. Relative cross sections for the two states σ(3/2) and σ(1/2) have been determined at three collision energies 0.2, 1.4, and 5.8 eV. It has been found that in Reaction (1), σ(3/2) is larger than σ (1/2) with ratio σ(1/2)/σ(3/2) ranging from 0.5 to 0.8 depending on the collision energy, whereas in Reaction (2), σ(1/2) is larger than σ(3/2) with the ratio ranging from 1.2 to 1.6. The implications of these results are discussed with regard to the roles of energy resonance and Franck–Condon factors in charge transfer processes.

State selected ion–molecule reactions by a TESICO technique. II. Separation of the reactant spin–orbit states in the reaction Ar+(2P3/2, 2P1/2)+H2(D2)→ArH+(ArD+)+H(D)

Cross sections for the atomic rearrangement reaction Ar++H2(D2)→ArH+(ArD+)+H(D) [Reaction (1)] and the charge transfer reaction Ar++H2(D2)→Ar+H+2(D+2) [Reaction (2)] have been determined for each of the Ar+ spin–orbit states (2P3/2 and 2P1/2) separately in the collision energy range from 0.05 to 0.5 eV (c.m.), utilizing the threshold electron–secondary ion coincidence (TESICO) technique which we developed recently. It has been found that the cross sections of Reaction (1) are larger for the 2P1/2 excited state than for the 2P3/2 ground state by a factor of 1.5 (with H2) and 1.3 (with D2), regardless of the collision energy in the range studied. The cross sections for both the H2 and D2 reactions show an approximately E−1/2.5 collision energy dependence which is somewhat milder than that expected from the simple Langevin theory. The cross sections of Reaction (2) have been found to be about seven times larger for the 2P1/2 state than for the 2P3/2 state with H2, whereas these are almost the same for both s...

State selected ion–molecule reactions by a TESICO technique. V. N2+(v)+Ar→N2+Ar+

Charge transfer reactions N2+(v)+Ar→Ar++N2 (1) have been studied by selecting the vibrational states of N2+ using the threshold electron–secondary ion coincidence (TESICO) technique. Relative cross sections σ(v) for the individual vibrational states v = 0–3 have been determined at three collision energies, 0.3, 1.5, and 11.8 eV. Results show that Reaction (1), which is endoergic for v = 0, is considerably enhanced by the vibrational excitation of N2+ at all collision energies. While excitation of one vibrational quantum enhances the cross section substantially, excitation of additional quanta further increases the cross section up to v = 3. The ratios σ(2)/σ(1) and σ(3)/σ(2) are, however, much smaller than σ(1)/σ(0) and are significantly larger at the highest collision energy than at the other two collision energies. These results are discussed in conjunction with the calculated results based on the simple two‐state theory of Rapp and Francis and the Franck–Condon factors.