화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.104, No.48, 11278-11281, 2000
Field-dependent relaxation and molecular reorientation of C-60 in chlorobenzene
To advance our understanding of the C-13 spin-lattice relaxation process and rotational dynamics of C-60 in various environments, we have acquired relaxation data on this molecule in chlorobenzene-d(5) as a function of field strength and at various temperatures. Field-dependent measurements allowed us to separate the contributions arising from the two possible modes for relaxation in this molecule: chemical shift anisotropy (CSA) and spin-rotation (SR). The CSA and SR values were used to extract the reorientational time, tau (c), and the angular momentum time, tau (J), which allowed us to investigate the rotational dynamics of C-60 in this solvent. We found that the longitudinal relaxation rate is dominated by the chemical shift anisotropy mechanism and that spin-rotation becomes rapidly more important with rising temperature. This is seen especially at 4.7 T, where SR dominates at the moderate temperature of 333 K. We also compared our field-dependent findings with values derived via the Hubbard relation, and we have found the Hubbard approach to overestimate the CSA contribution, causing underestimation of the SR effect. Finally, in an attempt at characterizing our experimental correlation times, we applied the Stokes-Einstein-Debye (SED), Gierer-Wirtz (GW), and Hynes-Kapral-Weinberg (HKW) models to our system and found their predictions to be inconsistent with our experimental findings. Far better agreement was obtained with the GW and HKW theories when these models were expanded to account for the inertial contribution to the overall rotational time. Our investigation also revealed that C-60 reorients in the intermediate regime rather than at either the "slip" or the "stick" extremes.