The dipole moment function for the X 2Σ+ state of AlO has been determined by a convergent sequence of MCSCF and CI calculations. It is nearly constant between R = 3.0 and 4.Oa0 because of a gradual transition from Al+O- to Al ++O--. This leads to a small vibrational band oscillator strength of f01 = (4.0±3.0) × 10-7. Several MCSCF models were tested for their ability to describe the charge transfer process, and the best model was used to study the B 2Σ + state AlO. © 1982 American Institute of Physics.