Negative ions of polar molecules

The influence of a molecule's dipole moment on its ability to capture an electron into a stable bound state is examined. It is proved that, in the fixednuclei approximation, a value greater than 1·625 Debye for the dipole moment suffices to guarantee the existence of a discrete spectrum of negative ion states. Implications for Hartree-Fock calculations of negative ions are discussed. The interaction of electronic, vibrational and rotational motions in negative dipolar ions is studied, and conclusions are drawn for real molecules.