Electron exchange between a dipole-bound anion and a polar molecule and dimer formation in dipole-bound anions

Abstract

We consider collision between a dipole-bound molecular anion and a neutral polar molecule and show that the excess electron can bind two neutral molecules into a dimer. Using a variational approach similar to the Heitler-London model of $\text{H}_{2}{}^{+}$ ion, we obtain the energy terms of such a dimer. Their difference determines the cross section of electron transfer from the anion to the neutral molecule in quasiclassical near-resonant Born-Oppenheimer approximation. We obtain for the cross section an analytical expression containing the weak (logarithmic) factor depending on the molecular dipole moment and the collision velocity. With the prelogarithmic factor proportional to inverse binding energy of the electron in the molecular anion, such weak dependence on the collision velocity is somewhat similar to the expressions appearing in the hard-sphere collision model. However the large logarithmic factor connected with long-range dipole-dipole interaction between the colliding molecules contradict to the hard-sphere approximation even for qualitative description of the charge transfer. Our analytical calculations are in a good accordance with the results of a recent experiment [Y. Liu, M. Cannon, L. Suess, F. B. Dunning, V. E. Chernov, and B. A. Zon, Chem. Phys. Lett. 433, 1 (2006)].