Electronic Transition Dipole Moment and Radiative Lifetime Calculations of Sodium Dimer Ion-Pair States

Alkali dimer M2 and alkali hydride MH molecular electronic states with ion-pair character are known to exhibit multiple minima and shoulders in their potential energy curves. This exotic behavior of the of the 1$\Sigma $g$+$ symmetry states is caused by an avoided crossing of the zero-order covalent and ionic (M$+ \quad + \quad$ M$-$) potential energy curves. We present a computational study of lifetimes and transition dipole moment matrix elements for the sodium dimer ion-pair states of 1$\Sigma $g$+$ symmetry. We report here the ab initio calculated electric transition dipole moments between the n 1$\Sigma $g$+$ and the A1$\Sigma $u$+$ states , that vary strongly as a function of internuclear distance. In addition, we have calculated the radiative lifetimes, $\tau $, of these ion-pair states of and compared them with the experimental results from literature when available.