Extended Coulomb approximation for multichannel-quantum-defect-theory computations of dipole moments: Method of calculation and application to H-2

A method for calculating dipole transition moments in effective one-electro n systems when some channels are closed is investigated within the framewor k of multichannel quantum-defect theory (MQDT). A treatment of the energy d ependence is also given. This method is useful when electronic channel inte ractions occur and MQDT is combined with frame transformations. Our calcula tions are made in the Coulomb approximation and include provisions for core transitions. They are tested by comparing transitions between bound states of molecular hydrogen with ab initio computations. [S1050-2947(98)039 12-2 ].