Proton Spin Relaxation and Molecular Motion in Liquid Thiophene

Abstract

Proton spin relaxation and molecular motion in liquid thiophene are studied in the temperature range 300–550°K by measuring spin—lattice relaxation time, T1, and the coefficient of self-diffusion, D, using spin—echo technique. The value of T1 varies from 24.0 sec at 300°K to 72.0 sec at 550°K with a maximum of 94.0 sec at 490°K. The value of D varies from 2.4× 10−5cm2/sec at 300°K to 38.0× 10−5cm2/sec at 550°K. These results have been analyzed in terms of three relaxation mechanisms: inter and intramolecular dipolar interactions and spin—rotation interactions. The analysis shows that (i) the rotational diffusion constant perpendicular to the plane of the molecule varies from 0.21× 1011sec−1 at 300°K to 3.5× 1011sec−1 at 550°K and obeys an Arrhenius equation up to 500°K with an activation energy 3.2 kcal/mole, (ii) the value of the angular velocity correlation time varies from 1.4× 10−14sec at 300°K to 10.8× 10−14sec at 550°K. An estimate of the spin—rotation interaction constant gives 13TrC≲ 1.0 kHz. The reorientational motion is found to be diffusional up to about 480°K.