SPIN-ASSISTED MATTER FIELD COUPLING AND LANTHANIDE TRANSITION INTENSITIES

For atoms with a central field in the Dirac-Foldy-Wouthuysen-Tani form alism, we find that an El matter-field coupling of the form qs . angst rom x p/2m2c2 appears with qangstrom . r in the length gauge. In princ iple, this gives an alternative source of spin-assisted contributions to lanthanide transition intensities. Time reversal and parity selecti on rules are used to categorize such contributions as well as those fr om the standard terms in the Judd-Ofelt theory of lanthanide transitio n intensities.