Electrons weakly bound to molecules by dipolar, quadrupolar or polarization forces

the framework of a simple electrostatic model we here discuss the stability of weakly bound molecular negative ions. In contrast with the case of conventional valence , the excess electron is then located in a very diffuse orbital and is mainly bound by dipolar, quadrupolar and polarization forces at large distances from the neutral core. By fitting a single repulsion parameter of the model to the available data, it is possible to make quantitative predictions of the excess electron binding in these species. Critical values of dipole moment, quadrupole moment or required for the observation of stable dipole-bound, quadrupole-bound or -bound negative ions are predicted.