Nuclear quadrupole double resonance

The development of double nuclear resonance techniques has allowed the detection of the nuclear quadrupole resonance (N.Q.R.) of many light elements which would have been impossible only a few years ago using conventional techniques. The apparatus is simple and easily automated and the methods yield good resolution combined with high sensitivity. Under the impact of these new techniques it appears likely that N.Q.R. will play a rapidly increasing role in the investigation of the internal electronic structure of solids. The various methods available are reviewed and those most suitable for N.Q.R., namely, Double Resonance in the Laboratory Frame (D.R.L.F.), Double Resonance by Level Crossing (D.R.L.C.), Double Resonance by Continuous Coupling (D.R.C.C.) and Double Resonance by the Solid State effect (D.R.S.S.) are examined in detail. The required theory is developed together with a description of experimental procedures and aids to the assignment of the spectra obtained. An apparatus suitable to employ the techniques is described. Listed in an appendix are the frequencies of the nuclear quadrupole resonance lines measured to date using the new techniques along with the deduced quadrupole coupling constants. Included are the spectra for over 200 different 14N sites, over 100 different 2D sites together with some spectra of 10B, 11B, 17O, 23Na, 25Mg, 27Al and 39K. (Auth.)