Example: electronic activation-deactivation in atomic collisions O(1D) + Ar <-> O(3P) + Ar
Electronic energy transfer in atomic collisions plays an important role in nonequilibrium gaseous systems, such as medium of gas lasers, low-pressure gas discharge, and upper atmosphere. Activation-deactivation O(3P) + Ar(1S) « O(1D) + Ar(1S) provides a typical example of such process.
The rate constants of the electronic activation-deactivation processes were evaluated using the Landau-Zener model. This model allows the calculation of rate constants of nonresonant energy transfer due to nonadiabatic transitions at the crossings or pseudo-crossings of electronic potential curves of diatomics corresponding to initially different electronic states of colliding atoms. As can be seen in the left figure, in the process under consideration, there occur three such crossings contributing to the overall rate constant. The electronic potential curves of the O-Ar diatomic and nonadiabatic couplings between the corresponding electronic states, necessary for applying the Landau-Zener model, were taken from the work [Cohen J., Wadt W., and Hay P., J.Chem.Phys. 71, 2955 (1979)], in which they were calculated by quantum-chemistry methods.
The calculated rate constant of the deactivation process and the available experimental data are presented in the right figure. It can be seen that the Landau-Zener model with the parameters obtained from quantum chemical calculations provides quantitative description of electronic quenching in atomic collision.
- Electronic potential energy curves of the diatomics O(3P) + Ar(1S) and O(1D) + Ar(1S).
- Calculated and measured (Lin M.C. Adv. Chem. Phys. 42, 113 (1980)) overall rate constant of the process O(1D) + Ar(1S)->O(3P) + Ar(1S).
