Extended diffusion theory of reorientation of symmetric top molecules with internal rotation: application to mesitylene

Our general extended diffusion theory for the reorientational dynamics of a symmetric top molecule with internal rotation is applied to mesitylene which is an oblate symmetric top. The basic idea of independent extended J-diffusion of both the overall and internal rotations with the different angular momentum correlation times is implemented in the theory. The resulting expressions for the dipole-dipole relaxation times for 13C nuclei are evaluated numerically and compared with NMR experiments on mesitylene. The angular momentum correlation times obtained from the comparison show that internal rotation is much faster than the overall rotation.