Abstract
For atoms with a central field in the Dirac-Foldy-Wouthuysen-Tani formalism, the authors find that an El matter-field coupling of the form qs.A*p/2m2c2 appears with qA.r in the length gauge. In principle, this gives an alternative source of spin-assisted contributions to lanthanide transition intensities. Time reversal and parity selection rules are used to categorize such contributions as well as those from the standard terms in the Judd-Ofelt theory of lanthanide transition intensities.