Abstract
Nitro groups are characterized by NQR lines of low intensity, since they lie in the 0.5-1 MHz frequency range. For example, in the cases of 1,3,5,7-tetranitro-l,3,5,7-tetraaxacyclooctane and cyclotrimethylenetrinitramine [i0, ii], it was not possible to detect the NQR spectra of the nitro groups with the aid of direct pulse NQR. Nevertheless, 14N NQR lines for the cyclic nitrogen atoms in these compounds were observed at 289 K at frequencies equal to 5300, 5063, 3737, and 3623 kHz and at 5192 and 3410 kHz (the most highfield lines). These lines are sufficiently intense to be observed in industrial mixtures of the compounds indicated with trinitrotoluene. With the aid of the spiral surface of the coil, direct pulse NQR [3] makes it possible to obtain a noticeable 14N signal from 1 kg of a mixture at distances up to 20 cm, even if the sample is located underground[2].
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