1. Kevan, L., and Kispert, L. D. 1976, Electron Spin Double Resonance Spectroscopy, John Wiley & Sons, New York.
2. Freed, J. H., and Dorio, M. M. 1979, Multiple Electron Resonance Spectroscopy, Plenum Press, New York.
3. Freed, J. H. 1969, J. Chem. Phys. 50, 2271.
4. Dalal, N. S., and McDowell, C. A. 1970, Chem. Phys. Lett. 6, 17.
5. For a recent review, see K. Mobius and R. Biehl in ref. 2, p. 475.