i.e., time averages are performed on the products of the projection cosines, 𝑙 𝑖𝑗 , of the three PAS axes in the lab frame. The matrix elements of the averaged Liouvillian and the relaxation matrix can then be calculated using the principal values of the motionally averaged tensor, 𝐕 A . In particular, the averages of the time-dependent frequencies of Eq. ( ) can be written: