Three-body ion-neutral association

Abstract

Consideration is given to the calculation of the rate coefficient of processes of the type A + + B + C → AB + + C. Classical mechanics is used. The impulse approximation is adopted and hard-sphere interactions are taken to describe C – A + and C – B collisions. Formulae are derived for the rate coefficients of binary collisions giving specified changes in the internal energy of the associating pair (without reference to their orbital angular momentum) and also of binary collisions giving specified changes in both the internal energy and in the square of the orbital angular momentum. By using quasi-equilibrium statistical theory, the rate co­efficient for three-body ion-neutral association is expressed in terms of either set of binary rate coefficients. Computations are carried out only Hg + + Hg + He → Hg + 2 + He. As expected, the predicted rate co­efficient is too high if specific account is not taken of the orbital angular momentum. If such account is taken excellent agreement is obtained with a measurement at 370 K made by Biondi (1953, 1972, private com­munication). The rate coefficient falls off slowly as the temperature is increased.