N-14 FOURIER-TRANSFORM NUCLEAR-QUADRUPOLE RESONANCE - INSTRUMENTATION - MEASUREMENTS ON CYANURIC CHLORIDE

A Matec pulsed instrument, already equipped with a laboratory-built data system, has been considerably improved by adding new capabilities, such as versatile pulse sequence programming. Among other things, this allows automated T1 relaxation measurements. The instrument has been employed to record the N-14 NQR FT spectrum of cyanuric chloride and measure its T1 relaxation time from 77 K to the melting point at 418 K. The four-line N-14 spectrum indicates the presence of two chemically inequivalent sites. The intensity ratio of the lines identifies the site pertaining to a couple of symmetry-related N-14 nuclei. The lines smoothly decrease in frequency up to the melting point, where they remain narrow and almost equally spaced. Considering previous results at 4.2 K, this indicates that a single phase is stable over the entire accessible temperature range. The relaxation time T1 decreases smoothly with increasing temperature, with a T-2 law, from nearly 180 s at 77 K to about 1 s near the melting point, where a precipitous decrease starts. The high T1 values found are consistent with the lack of nuclei having high magnetic moment.