Electron-neutral species interaction potentials

The Boltzmann equation works reasonably well when electrons collide mainly with neutral species. Electron-electron or electron-ion collisions involve coulombic interactions that have a longer range than that of electron-neutral species interactions. Coulombic-interaction potentials vary inversely with separation, but electron-neutral species interaction potentials vary inversely with the fifth or sixth power of separation. 

Stable protonated isomers are associated with minima of A mol. A first-order approximation predicts that protonation occurs at places where the molecular electrostatic potential is a minimum.22 Since, in neutral species, negative values of the electrostatic potential are usually associated with lone pairs or electron-rich regions,23 this approximation is very rational. At this level, the change in the energy, A/q R,) electrostatic interaction of the proton with the nuclei and the unperturbed electron density. Relaxation of the density, induced by the presence of the proton, is taken into account by higher-order terms. The second-order term, related to the density response kernel, contributes with an additional stabilization from the initial response of the density to the new positive charge. At the present, there is no simple procedure to compute the response kernels, neither its contributions to energy, and fundamental studies on this direction are desired. 

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