Three-frequency nuclear quadrupole resonance of spin-1 nuclei

We introduce a new nuclear quadrupole resonance (NQR) method for the detection of spin-1 nuclei, where the transition excited and directly detected is not irradiated at all. It is demonstrated, theoretically and experimentally, that the irradiation of a powder sample containing spin-1 nuclei by two of the three characteristic NQR frequencies can result in free induction decay (FID) and echo signals at the third NQR frequency. We present the optimal conditions for such three-frequency NQR experiments and compare theory with experiment using 14N (I=1) in a powder sample of sodium nitrite.