Example: ion-molecule reaction AlCl₂ + AlCl₃^– -> AlCl + AlCl₄^–

Bimolecular ion-molecular chemical reactions play an important role in the kinetics of discharge in molecular gases. In particular, in the discharge in a metal-halide/Ar mixture, metal atoms form not only through the direct dissociation of metal halide molecules by electron impact, but as a result of two extra channels of the conversion of polyatomic metal halide precursors to radiating atoms and diatomic molecules.

The reaction AlCl₂ + AlCl₃^– -> AlCl + AlCl₄^– is a typical example of such ion-molecular reactions. The potential energy profile of this reaction was obtained in Kintech Lab by ab initio calculations at the DFT level of theory using the GAUSSIAN 2003 program package. This energy profile is presented in the figure. It can be seen that this reaction proceeds via intermediate complex Al₂Cl₅^–. This situation was described within the statistical model of bimolecular ion-molecular reactions, and the rate constant of this reaction was calculated. The potential barrier occurs in the exit channel, but it is considerably lower than the energy level of the reagents. Therefore, the calculated rate constant is virtually independent of temperature and pressure and is equal to 3.5*10^–10 cm³/s.

Thus, the diversity of models and Kintech Lab expertise in quantum chemistry allowed us to gain quantitative information about the rate of a practically important ion-molecule reac­tion, for which both experimental and theoretical data were unknown.