Kaoru Matsuura

Nature and origin of nonresonant microwave response in ESR measurements of YBa2Cu3O7−δ

Abstract The nonresonant microwave response observed in the ESR measurements of YBa 2 Cu 3 O 7−δ was studied as a function of various ESR parameters. Its nonresonant nature was confirmed by an experiment and a theoretical calculation of the ESR-transition probabilities for parallel and vertical microwave polarizations. Field modulation dependence revealed that it was composed of two components: one is proportional to the modulation amplitude ( H m ) and has the same polarity upon the sweep reversal of DC magnetic field. The other is only observed during sweep. It has opposite polarity and is proportional to H m only in a narrow H m range. Their reference-phase dependences indicated that both components were mainly out-of-phase microwave responses. The theoretical analysis of these behaviors and the modulation scheme implied that the two components were microwave responses to the static and dynamic magnetizations trapped in the bulk and at intergranular Josephson junctions, respectively, providing a method for the separation of the two kinds of trapped magnetization.

Separation of magnetizations in the bulk and at Josephson junctions of Tl and Bi oxide superconductors using ESR spectrometers

Abstract The present work reports the trapping sites and trapping strength of magnetizations ( M ), which govern the superconductivity under magnetic fields, for Tl 2201 , Tl 2212 , Tl 1223 , Tl 1234 and Bi 2212 superconductors using ESR spectrometers. In the Tl compounds, M was trapped in the bulk and at intergranular Josephson junctions at 77 K except for Tl 2201 where it was trapped only in the bulk. For Bi 2212 M was trapped in the bulk and the junctions did not work as trapping sites at 77 K, although they worked at 4.2 K. The silver-metal doping in Bi 2212 provided stronger junctions than the non-doped Bi 2212 at 4.2 K; however, they were weak even compared with Tl compounds except for Tl 2201 at 77 K. The present method of separating magnetizations is based on a finding of two kinds of non-resonant microwave responses, whose assignments were confirmed by comparing type I and type II superconducting states using lead metal.

Stabilization and EPR characterization of Ru(bpy)33+ formed by radiolysis in concentrated alkali-metal halide solutions

The stabilization of Ru(bpy) 3 3+ from Ru(bpy) 3 2+ at room temperature by radiolysis of acidic concentrated alkali-metal halide aqueous solutions has been achieved. Stabilization at room temperature is of particular interest for potential light-energy storage systems. The yield of Ru(bpy) 3 3+ , as well as its half-life, depend strongly on the alkali-metal halide and acid concentrations. The Ru(bpy) 3 3+ yield increases with increasing LiCl concentration and attains a maximum value around 5–10 mM H + ; the yield decreases at both higher and lower pH. The stabilization of Ru(bpy) 3 3+ is optimal at [LiCl] 4 M and 5 mM H + . The half-lives of Ru(bpy) 3 3+ are 20 h and 7 days at [LiCl] = 4 and 8 M, respectively, which are ca. 10 to 100 times longer than in a solution without LiCl. The stability of Ru(bpy) 3 3+ also depends on the alkali-metal cation. The half-lives of Ru(bpy) 3 3+ vary from 7 to 20 h in the order K, Na and Li at 5 mM H + and 4 M alkali-metal halide solution. This cation effect on the stabilization of Ru(bpy) 3 3+ is interpreted in terms of the free water concentration and dynamic hydration properties in alkali-metal halide solutions.

The role of alkyl substitution on the spin distribution in the radical cation of alkyl-cyclohexane: An electron-spin-resonance study

The role of alkyl substitution on the electronic structure of cyclohexane radical cation was investigated with low-temperature matrix ESR and semiempirical MO calculations. It was found that the unpaired electron, which is originally delocalized throughout the cyclohexane ring, tends to be confined to one of the CC σ-bonds in the ring at the position of the alkyl substitution. When the alkyl chain is longer (NC⩾4), the unpaired electron tends to flow out from the ring to the side chain. Based on these findings, the difference between the alkyl-substitution effects on the electronic structures of an aliphatic and an aromatic Jahn-Teller active cyclic cation is discussed.

Vibronic spectrum and structure of the trans‐bent acetylene radical anion

We report the first observation of the vibronic absorption spectrum of the trans‐bent acetylene radical anion, produced in 3‐methylpentane matrices by γ irradiation at 77 K. Two optical absorption bands are observed at 300–360 nm and in the region λ<420 nm. The former (strong) and the latter (weak) bands correspond respectively to electronic transitions to the Ψ2(Bu) and Ψ1(Au) excited states, specifically to the vertical transitions ‖pπy*(C≡C)〉←‖pπy(C≡C)〉 and ‖pπy*(C≡C)〉←‖πz(C≡C)〉 from the ground state ΨG(Ag) having an in‐plane pseudo π* type singly occupied molecular orbital: ‖pπy*(C≡C)〉. For the 12C2H2− anion, these bands are accompanied by a single‐vibrational progression of 1300–1240 (±20) and ∼1150 (±60) cm−1, respectively. These progressions are assigned to the (v←0) transitions of C≡C stretching modes and to H–C≡C–H bending vibrational modes by comparison with the results for 13C2H2− and 12C2D2− anions. The appearance of only a single‐vibrational mode is reasonably well understood, from a molecula...

First observation of alkyne radical anions by electron spin resonance spectroscopy: Hexyne/ n -hexane mixed crystals

The radical anions of alkynes have been first observed by electron spin resonance spectroscopy following alkene anions previously studied. Hexyne radical anions were formed in 1‐, 2‐, or 3‐hexyne/n–hexane mixed crystals irradiated at 4.2 or 77 K. The characters of the anions were as follows; (a) the α‐proton hyperfine coupling is very large (∼4.5 mT for the 1‐hexyne anion), (b) the β‐proton couplings are very small (∼1.0 mT for C–Hβ proton with the conformational angle of 0°), and (c) the radicals show a negative g shift (2.0014). From these observations, it was found that the anions have a nonlinear(bent) molecule structure in the anticonfiguration (trans C–C≡C–C) with the bend angle ∼60°, and that the unpaired electron orbital is approximately composed of the anticombination of the sp2 hybrid orbitals of the C≡C carbon atoms. A discussion based on complete neglect of differential overlap (CNDO) molecular orbital (MO) calculations was given for the observed negative g shift, which was shown to be charact...

An ESR and NMR study of the radiolysis of n-alkanes: Crystal structure dependence

The process of radiation damage for long-chain n-alkanes was investigated to elucidate that for polyethylene. Chain-end alkyl radicals were preferentially formed not only through primary C-H scission but also through a hydrogen atom reaction in odd-n-alkane, as was shown by analysis of the ESR spectra for isotopic mixtures of tridecane-h28/tridecane-d28 and nonadecane-h40/nonadecane-d40. To elucidate the mode of alkyl radical migration in solids through intermolecular hydrogen atom abstraction, D/H exchange was detected in mixed crystals of eicosane-d42/eicosane-h42. The chain-end region was found to be more reactive than the inner region for radical site migration. In addition, formation of a microscopic amorphous island by destruction of the crystal lattice was also detected. The influences of molecular packing were large in all cases.

Separation of magnetizations in the bulk and at Josephson junctions of superconductors by analysis of microwave responses detected using an improved ESR spectrometer

Abstract The present study provides an improved ESR spectrometer and a useful method which make it possible to separate two kinds of magnetizations trapped in the bulk and at Josephson junctions of superconductors, based on the characteristics of two component microwave responses previouly found.