New Methods for Detection of 14N NQR Frequencies

Abstract

Nitrogen atoms are present in a number of solid explosives and illicit substances. The nuclear quadrupole resonance (NQR) spectra and spin–lattice relaxation of the nitrogen atomic nucleus 14N can be used to characterize these compounds and to distinguish between possible crystal polymorphs. After the characteristic 14N NQR frequencies and spin–lattice relaxation rates in a compound are determined, NQR can be used to detect this compounds and, in case of crystal polymorphs, also to determine the method of preparation. The 14N NQR frequencies and spin–lattice relaxation rates are measured either by pulse NQR or by nuclear quadrupole double resonance (NQDR) based on magnetic field cycling. Here, we discuss several 1H–14N NQDR techniques which can be used to measure the 14N NQR frequencies and spin–lattice relaxation rates under various experimental conditions. Some characteristic applications of these techniques are presented and discussed in details.