OPTICAL DIPOLE TRANSITIONS BETWEEN ADJACENT STATES

It is shown that, for optical dipole transitions between states which are degenerate in the limit of the nuclear charge Z being infinite, the dipole length formula is likely to give greater accuracy than the dipole velocity and dipole acceleration formulae. Formulae which are exact to O(1/Z3) are given for the transition matrix elements for the 2 1S-2 1P and 2 3S-2 3P transitions in the two-electron systems.