Nuclear quadrupole resonance

Nuclear quadrupole resonance is a recently developed branch of radio-frequency spectroscopy which is concerned with magnetic resonance absorption in crystals. This absorption is due to reorientation of the nonspherical atomic nuclei against crystalline electric fields. Related phenomena in isolated molecules are briefly mentioned in the Introduction A. This is followed in Sec. B by an elementary treatment of the electrostatic interaction of a nonspherical nucleus with an axially symmetric inhomogeneous electric field as is found approximately in crystalline Cl2, a crystal whose structural units are very nearly undisturbed Cl2 molecules. Electrostatic torques are shown to exist which cause a precession of the nuclear angular momenta around the molecular axes. As this motion is accompanied by a precession of the magnetic and electric moments of the nuclei, which may interact with alternating electromagnetic fields, this leads over to the transition mechanism between the energy levels which are obtained from...