title: The low-temperature 13C and 2H spectra and relaxation rates of methyl groups depend on the azimuth of B0 in the molecular frame. Those of 1H do not. Why?
abstract: It is shown that the answer to the question asked in the title is: Because the axial symmetry axes of the H-H dipolar coupling tensors in a -CH3 group are perpendicular to the (assumed) threefold axis of the group. By contrast, those of the 13C-H dipolar and 2H quadrupolar coupling tensors are not. The use of "symmetry adapted" spin functions and of a symmetry adapted form of the (dipolar) coupling Hamiltonian greatly simplifies the analysis.
authors.affiliation: SAP AG, Neurottstr. 16, 69190 Walldorf, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Gutsche
authors.forename: U
authors.initials: U
authors.lastname: Haeberlen