Stark effect measurements on the NaK molecule

In a newly built molecular beam apparatus we have measured permanent electric dipole moments of the B (1) I and X (1) I pound (+) states of NaK to test the vibrational dependence of the dipole moment function as predicted by ab initio calculations by Aymar and Dulieu [J. Chem. Phys. 122, 204302 (2005)]. Four vibrational bands were studied, the dipole moment for the B (1) I decreases from 2.73(2) D for v = 3 to 1.99(2) D for v = 13. The vibrational dependence shows a fairly good agreement with theory, but the absolute values are lower than those from the calculation by 13%. The ground state dipole moment of 2.72(6) confirms the earlier result by Wormsbecher et al. [J. Chem. Phys. 74, 6983 (1981)].