We present a new analysis of the electron capture mechanism in polar molecules, based on von Neumann's theory of self-adjoint extensions. Our analysis suggests that it is theoretically possible for polar molecules to form bound states with electrons, even with dipole moments smaller than the critical value D0 given by 1.63 × 10 −18 esu cm. This prediction is consistent with the observed anomalous electron scattering in H2S and HCl, whose dipole moments are smaller than the critical value D0. We also show that for a polar molecule with dipole moment less than D0, typically there is only a single bound state, which is in qualitative agreement with observations. We argue that the quantum mechanical scaling anomaly is responsible for the formation of these bound states.PACS numbers: 03.65. Ge, 31.10.+z, The experimentally observed anomalous scattering of electrons by a class of polar molecules [1,2,3] is often attributed to the electron capture by the dipole field of the polar molecules [4,5,6]. It is usually assumed that a dipole bound state of an electron is possible only if the coefficient of the inverse square interaction term is sufficiently negative, leading to a "fall to the centre" condition [7]. The point dipole model of the polar molecule predicts that the critical dipole moment [8] D 0 necessary for the electron capture has a value D 0 = 1.63 × 10 −18 esu cm [9,10,11,12], which continues to be valid for an extended dipole as well [9]. The captured electrons are usually weakly bound, which makes such bound states hard to detect unless the dipole moments are large compared to D 0 . Consequently, most of the experiments are performed with molecules having large dipole moments, for which the above value of D 0 is consistent with the experimental data.However, there are certain polar molecules, e.g. H 2 S and HCl which have dipole moments less than D 0 and yet exhibit anomalous electron scattering and can capture electrons [9,13]. The simple model of the inverse square interaction which predicts the above value of D 0 , at the first sight, seems to be inconsistent with the data for H 2 S and HCl. Moreover, the same theoretical model predicts an infinite number of bound states for dipole bound anions, whereas most experiments observe only a single bound state [14].We may think that these inconsistencies arise from the fact that the pure dipole model of a polar molecule ignores various short range interactions that play a role in the electron capture. However, the inverse square interaction between the electron and the polar molecule encodes the main aspects of the long distance dynamics leading to the formation of weakly bound states [11]. Within this approximation, and without using any detailed knowledge of the short distance interactions, it is reasonable to represent their effects through the boundary conditions obeyed by the Hamiltonian. Note that the molecular forces are usually not dissipative, and the corresponding Hamiltonian remains always self-adjoint [15]. Thus, the problem now reduces to finding al...