Abstract: | The potential energy curve and theoretical dipole moment function of the a4Π state of NO have been determined using full-valence and first-order configuration interaction wavefunctions. Using these two different wavefunctions, the dipole moments of the a4Π, v = 3 level have been found equal, respectively, to 0.16 D and 0.30 D, with the polarity N+O−. These values compare well with the value of |0.20 ± 0.04| D determined by Lisy and Klemperer. The first derivative of the dipole moment has also been calculated to be equal to 1.25–1.73 D/bohr. |