Abstract A LCAOMO calculation has been performed to calculate the values of both the dipole length (Qtheor.L) and dipole velocity (Qtheor.V) transition moments of the lowest energy t 1 → 2e ( 1 A 1 → 1 T 2 ) transition for the isoelectronic tetroxy anions (MoO4staggered2−, TcO4− and RuO4) of the second transition metal series in terms of a single parameter β, the ligand mixing coefficient using STO's and more exact AO's derived by Basch and Gray to duplicate as nearly as possible the SCF AO's. All contributions from charge transfer integrals, one-center ligand integrals and two-center ligand integrals have been considered. The use of dipole velocity operator leads to better results than those of the dipole length operator. As a by-product based on simplifying assumptions, the pertechnetate ion appears to possess less π-bonding than ruthenium tetroxide and molybdate ion has the least π-bonding.