Proton Spin Relaxation and Molecular Motion in Liquid Thiophene

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.