Masaharu Toyama

Effect of vibration and rotation on the internuclear distance

Abstract The effect of vibration and rotation of a molecule on the internuclear distances is calculated to the second order of approximation. A general formula for the expectation value is obtained including the effects coming from the anharmonicity of vibration as well as from the centrifugal force. Coriolis coupling has influence neither on the internuclear distances in the ground state nor on the averaged distances in the thermal equilibrium. Convenient expressions for the centrifugal distortion are considered by making use of vector notations. Actual calculation for individual molecules has revealed many changes in the average positions of the nuclei, particularly in the molecules containing hydrogen atoms. The statistical average of the internuclear distance in thermal equilibrium is calculated. It is seen that the change in the internuclear distance due to centrifugal distortion is proportional to the temperature. The anharmonic vibrational effect is more significant than the centrifugal distortion.

Zeeman Effect of the Nuclear Quadrupole Resonance Spectrum in Crystalline Powder

The Zeeman effect of the nuclear quadrupole resonance spectrum for spin I=32 in crystalline powder has been studied. Theoretical considerations have predicted that, in a nonaxial electric field gradient, the absorption line should be broadened with a characteristic envelope by a weak static magnetic field. When a radio‐frequency (rf) field is applied parallel to the static field, one pair of sharp minima should be produced on the envelope at the frequencies shifted by ±γH/2π from the unperturbed quadrupole resonance line, and two pairs of sharp maxima at ±(1−η)γH/2π and at ±(1+η)γH/2π. Resonance spectra of Cl35 nuclei in p‐dichlorobenzene and cyanuryl chloride have clearly displayed the predicted shape of envelopes on a recorder at room temperature. Analysis of them has resulted in determining the asymmetry parameters of electric field gradients with considerable accuracy; 0.070±0.01 for the α‐modification of p‐dichlorobenzene, and 0.22±0.03 for ν1 line, and 0.23±0.04 for ν2 line of cyanuryl chloride.

Zeeman Effect of Nuclear Quadrupole Resonance Spectrum in Cyanuryl Chloride

A study on the Zeeman effect of Cl 35 nuclear quadrupole resonance spectrum was carried out on a single crystal of cyanuryl chloride. Three distinct q -tensors were found in this crystal, two of them being equivalent. The directions of the principal axes were determined within the accuracy of 1° . It was concluded that in the crystal all molecules are disposed parallel (or antiparallel) to one another and three C–Cl bonds of a molecule are on a plane, making an angle 120° with one another, one of them being not equivalent to the other two. A large asymmetry parameter, 0.26, was obtained. From the coupling constant and the asymmetry parameter, the double bond character and the ionic character of C–Cl bonds were estimated to be 10% and 17%, respectively. The large double bond character was considered to be associated with the large electronegativity of nitrogen atoms in the ring.

Relative Intensities of Zeeman Components in Nuclear Quadrupole Resonance Spectrum

The transition probabilities for the Zeeman components in nuclear quadrupole resonance spectrum were formulated in the case of arbitrary field gradient. Interesting behaviours were revealed especially for a nucleus of half-integral spin. When a magnetic field is applied in a direction perpendicular to the principal z -axis in the case of nonaxial field gradient due to the surrounding charges, the inner pair of the Zeeman components is produced by the x -component of the rf field and the outer pair by the y -component. The dependence of the intensities on the Zeeman field is in general not symmetric with respect to the principal axes of the field gradient.

Zeeman Effect of Nuclear Quadrupole Resonance Spectrum in 1, 3, 5-Trichlorobenzene

A study of the Cl 35 resonance spectrum was carried out at the room temperature on a single crystal of 1, 3, 5-trichlorobenzene. Spatial orientation of the C–Cl bonds was determined to the accuracy of 1° . An orthorhombic structure was concluded, with the unit cell containing at least four equivalent molecules oriented with the symmetry of D 2 h . The angles between the C–Cl bonds in each molecule were close to the hexagonal angle, but one of the C–Cl bonds was deformed by ca. 1.6° from the plane of the other two. The asymmetry parameters were observed to be 0.09 3 , 0.11 1 , and 0.12 9 for three absorption lines, 35.020 Mc, 35.296 Mc, and 35.545 Mc, respectively. The results were discussed from the viewpoint of intermolecular interaction.

Acceptors and the Edge Emissions in CdS and ZnSe

The edge emission in CdS was studied, paying special attention to the acceptors involved. At least seven different exciton lines, which are believed to be related with the acceptors responsible for the edge emission, were found in the wavelength region between 4892.6A and 4876.8A in various crystals, indicating a wide range of ionization energies of the acceptors. The sample showing two acceptor exciton lines exhibits corresponding edge emissions relevant to these two acceptors. This was confirmed by the observation and analysis of the time-resolved spectra of these edge emissions. The variety of acceptor-bound exciton lines requires prudence for the identification of the chemical nature of the acceptors. Evidence is presented as to similar variety of the edge emission in ZnSe.

Electron Spin Resonance Parameters in 6H Polytype of Silicon Carbide Crystal Doped with Boron

Valence electrons of the boron atom substituting for carbon in 6H silicon carbide have been studied, for the purpose to elucidate the results of electron spin resonance experiment by Woodbury and Ludwig. A theoretical predict has been presented on the basis of tight binding approximation. Partial ionicity of the B-Si bond where the boron atom is positive has been proposed as an origin of small 11 B hyperfine interaction compared with 29 Si superhyperfine interaction. The opposite signs in the hyperfine constants A and B observed in one spectrum (called I) have been interpreted in terms of a weak trigonal field. Its potential for electron is lower in the direction of the B-Si bond parallel to the c axis. Such a trigonal field is demonstrated in the boron center occupying the site 9 d , to which the spectrum I is likely to be assigned. The calculation has also predicted the g || value to be identical to the free spins and the g ⊥ value to be slightly larger than it, in good agreement with the values observ...