Improving N nuclear quadrupole resonance detection of trinitrotoluene using off-resonance effects

The off-resonance dependence of the amplitudes of the six dominant ¹⁴N nuclear quadrupole resonance (NQR) lines in commercial polymorphic trinitrotoluene (TNT) sample were experimentally determined for a wide range of experimental parameters when irradiated with the spin-lock spin-echo (SLSE) pulse sequence. We find that the amplitudes off-resonance dependence follows a sinc-like function with an additional modulation due to the spacing between the RF pulses. This dependence can be very well modeled with expressions we have derived for a single site ¹⁴N NQR in paranitrotoluene (PNT). The results can be immediately used for the reduction of the number of free parameters used in the robust signal processing models for the TNT NQR detectors.