Pure Nuclear Quadrupole Spectra of Chlorine and Antimony Isotopes in Solids

Abstract

Experimental measurements on nuclear quadrupole resonances of chlorine and antimony isotopes in solids have been made to an accuracy of about 0.001 percent. The results are compared in detail with theoretical results for (1) nuclear quadrupole interaction, (2) interaction between quadrupole coupling and thermal vibrations, and (3) effects of a nuclear hexadecapole. The ratio $\frac{{\mathrm{}\left(\mathrm{eQq}\right)\mathrm{}}_{{\mathrm{Cl}}^{35}}}{{\mathrm{}\left(\mathrm{eQq}\right)\mathrm{}}_{{\mathrm{Cl}}^{37}}}$ varies between 1.268736 and 1.268973 while $\frac{{\mathrm{}\left(\mathrm{eQq}\right)\mathrm{}}_{{\mathrm{Sb}}^{123}}}{{\mathrm{}\left(\mathrm{eQq}\right)\mathrm{}}_{{\mathrm{Sb}}^{121}}}$ varies from 1.274714 to 1.274770. These variations may be attributed to zero-point vibrations and to thermal vibrations, so that no clear evidence is found for nuclear polarization by surrounding electric fields. For $p$-dichlorobenzene, the temperature coefficient of the coupling constant of Cl and the variation of isotopic coupling ratio with temperature are shown to be in fair quantitative agreement with the extension of Bayer's theory of vibrational effects. Relaxation times, Zeeman effects, and certain effects due to crystal structure are examined. Small discrepancies in the measured ratios of frequencies of transitions in ${\mathrm{Sb}}^{121}$ and ${\mathrm{Sb}}^{123}$, which can be attributed to nuclear hexadecapole interactions are found. These indicate a hexadecapole coupling constant in ${\mathrm{Sb}}^{123}$ of 24 kc/sec and a ratio of the ${\mathrm{Sb}}^{123}$ hexadecapole coupling to that of ${\mathrm{Sb}}^{121}$ of 0.8±0.3. A convenient high-sensitivity circuit for observation of nuclear resonances in solids has been developed and is discussed.