Quadrupole double resonance at high radiofrequencies

Irradiation close to a number of ³⁵Cl, ⁷⁹Br and ¹²⁷I quadrupole resonance frequencies in hydrogen-containing compounds at room temperature and radio-frequencies as high as 552 MHz is shown to produce considerable polarization of the protons. Despite the short relaxation times, these polarizations can be captured in a conventional double resonance spectrometer based on adiabatic demagnetization by imposing a “transfer” field of about 200 gauss whilst the sample is in flight from the low-field to the high-field coil. The technique is easily modified to provide rapid measurements of the ¹H spin-lattice relaxation times in low magnetic fields.