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 the Nuclear Quadrupole Resonance Spectrum in Crystalline Powder

Structure of molecules with large amplitude motion as determined from electron-diffraction studies in the gas phase

The pure quadrupole resonance spectra were observed on Cl 35 and Cl 37 in BCl 3 and Br 79 and B 81 in BBr 3 at several temperatures. The spectrum of each nucleus consists of characteristic doublet (ν I and ν II ) with the intensity ratio of ca. 3 to 5. The Zeeman study with a single crystal of BBr 3 was also carried out at liquid nitrogen temperature (77°K), to determine the asymmetry parameter η. The results are as follows:

Nuclear Quadrupole Spectra of Boron Trichloride and Tribromide

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.

Relative Intensities of Zeeman Components in Nuclear Quadrupole Resonance Spectrum

An experimental technique is developed for the measurement of asymmetry parameters in electric quadrupole coupling of nuclei with spin I32 in covalent bonds in organic single crystals. The theoretical details of Zeeman‐split nuclear quadrupole resonance spectra, upon which the technique is based, are examined and found to yield a particularly simple approximate expression for the asymmetry parameter of the electric field gradient tensor, which has been previously shown to be proportional to the double‐bond character of the covalent bond. The technique is applicable to atoms bound to a single neighbor in the organic molecule. The limitations of the approximations involved in obtaining the simple formula are examined in detail, and it is found that an order‐of‐magnitude smaller probable error may be obtained than has been possible with previous geometrical techniques. Correction formulas are presented which may yield still another order‐of‐magnitude better precision if desired. Experimental results on the C...

Covalent-Bond Asymmetries from Zeeman-Split NQR

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.

Takashi Shimozawa

Papers

Zeeman Effect of Nuclear Quadrupole Resonance Spectrum in Cyanuryl Chloride

Pure Quadrupole Spectra of the Isomers of Benzene Hexachloride

Dipole Moment and Internal Rotation of 1,4-Dichloro-2-butyne in the gaseous State

The Dipole Moments of Bromothiophenes

Pure Quadrupole Spectra of Propargyl Chloride and its Related Compounds