Effect of Large Quadrupole Interactions on Nuclear Radiofrequency Spectra at Twice Larmor Frequency

Abstract

The work of B. T. Feld and W. E. Lamb [Phys. Rev. 67, 15 (1945)] on the effect of a nuclear electrical quadrupole moment on the radiofrequency absorption spectrum of a heteronuclear diatomic molecule in a magnetic field is extended to a special case not considered by them. This is a case in which the electrical quadrupole interaction energy is so large that even in magnetic fields of several thousand gauss the magnetic interaction energies are small compared to the electrical quadrupole interaction energy. In this case it is shown theoretically that for a spin of $\frac{3}{2}$ there are certain circumstances under which a maximum of absorption will occur at double the Larmor frequency instead of at the Larmor frequency and will have a field and molecule dependence similar in many ways to a resonance at the Larmor frequency. This result has the important implication that special care must be used in identifying the radiofrequency resonance absorption spectra or an error of a factor of two in the value of a nuclear magnetic moment can easily be made. The approximate shape and intensity of the radiofrequency absorption spectrum under these circumstances is calculated in order that a comparison of the theoretical shapes and intensities with the experimental ones can be used as a means of recognizing if an absorption is a double Larmor frequency one.