The permanent electric dipole moment of NbN

A high resolution optical Stark study of a niobium nitride (NbN) supersonic molecular beam sample has been performed. The F′=2.5–F″=3.5 hyperfine component of the R(1) branch feature of the (0,0) B 3F2–X 3D1 subband system was recorded as a function of static electric field strengths up to 2.7 kV/cm. The permanent electric dipole moment of 3.26(6) D and 4.42(9) D for the X 3D1 and B 3F2 states, respectively. The properties of the X 3D1 state were calculated ab initio using a complete active space multiconfiguration self-consistent-field approach followed by first-order configuration interactions plus multireference singles+doubles configuration interaction treatment. The calculated dipole moment for the X 3D1 state at the experimentally determined equilibrium bond distance is 3.65 D.