Time evolution of proton magnetization in the spin-rotating frame of an ensemble of interacting pairs of methyl groups: A study of the magnetic-flux effect

Berry-phase calculation of magnetic screening and rotational g factor in molecules and solids

The orbital magnetic moment due to rotation or pseudorotation in a molecule or a solid and the corresponding rotational g factor are formulated using the Berry-phase technique and standard density functional plane wave methods. Among the simplest molecules, H+2, H2, C2H2, CH4, and CF4, with known rotational g factors, are used as test cases with excellent results. Alternative, faster localized orbital calculations including the magnetic coupling through heuristic Peierls phase factors are also tested and found to be viable, though less accurate. Application to pseudorotations is exemplified in benzene. It is proposed that these methods will be suited for application to pseudorotations in solids.

Spectroscopy from proton spin magnetization evolution in their rotating frame: A study of small tunneling splitting

The time evolution of proton Zeeman magnetization in the rotating frame at exact resonance, omega = omega(0), is evaluated for an isolated tunneling methyl group CH(3). The Fourier transform of this evolution in time is calculated and both its real and imaginary components are presented. It is shown that the real component does not depend significantly on the strength of the preparation pulse when the tunneling splitting of the methyl rotator ground state is less than 100 kHz. It is also found that the imaginary component of the transform is inversely proportional to the strength of the preparation RF pulse. This is a consequence of the partial dephasing of proton spins during the preparation pulse. The results of the calculation compare well with the experimental spectra of CH(3)CD(2)I.