Accurate spin-orbit splitting constants (A(v+)) for the vibrational levels v(+)=0-41 of CO+(A (2)Pi(3/2,1/2)) have been determined in a rotationally resolved pulsed field ionization photoelectron study. A change in slope is observed in the v(+) dependence for A(v+) at v(+)approximate to 19-20. This observation is attributed to perturbation of the CO+(A (2)Pi) potential by the CO+(B (2)Sigma(+)) state. Theoretical A(v+) values for CO+(A (2)Pi(3/2,1/2), v(+)=0-41) have also been obtained using a newly developed ab initio computational routine for spin-orbit coupling calculations. The theoretical A(v+) predictions computed using this routine are found to be in agreement with the experimental A(v+) values for CO+(A (2)Pi(3/2,1/2), v(+)=0-41). Similar A(v+) calculations obtained for O-2(+)(X (2)Pi(3/2,1/2g), v(+)=0-38) are also in accord with the recent experimental A(v+) values reported by Song [J. Chem. Phys. 111, 1905 (1999)].