Tidal termolecular ionic recombination

Measurements by Mezyk et al. (1989,1991) have shown that the rate coefficient for Xe2++Cl-+Xe to XeCl*+2Xe is enhanced relative to that given by the universal curve that describes termolecular recombination of structureless atomic ions. This is attributed to Cl- exciting internal modes of Xe2+ during passage through the perihelion part of the orbit. The electrostatic tidal effect is simulated by the Monte Carlo technique, excellent agreement with the data of Mezyk et al. being obtained. It is reasoned that the tidal action cannot enhance the rate of termolecular recombination of small valence-bound ions like O2+ and O2- appreciably. However its influence is pervasive because complex ions are commonly present when the ambient gas density is enough for termolecular recombination to be of interest: for example, O4+ is the main positive ion if the ambient gas is pure oxygen. Enhanced mutual neutralization may obscure the experimental evidence.