Abstract
The present Letter shows that the formation of ozone in ternary collisions O+O_{2}+M-the primary mechanism of ozone formation in the stratosphere-at temperatures below 200K (for M=Ar) proceeds through a formation of a temporary complex MO_{2}, while at temperatures above ∼700 K, the reaction proceeds mainly through a formation of long-lived vibrational resonances of O_{3}^{*}. At intermediate temperatures 200-700K, the process cannot be viewed as a two-step mechanism, often used to simplify and approximate collisions of three atoms or molecules. The developed theoretical approach is applied to the reaction O+O_{2}+Ar because of extensive experimental data available. The rate coefficients for the formation of O_{3} in ternary collisions O+O_{2}+Ar without using two-step approximations were computed for the first time as a function of collision energy. Thermally averaged coefficients were derived for temperatures 5-900K. It is found that the majority of O_{3} molecules formed initially are weakly bound. Accounting for the process of vibrational quenching of the nascent population, a good agreement with available experimental data for temperatures 100-900K is obtained.
Highlights
In this Letter, we present a direct three-body recombination approach to studying the formation of ozone without invoking the formation of an intermediate complex
The application of this method to the formation of ozone via ternary recombination reaction O2 þ O þ Ar → O3 þ Ar is based on the assumption that the internal degrees of freedom of the oxygen molecule do not play an essential role since the excitation of the O2 vibrational mode requires high collision energy over 1000 cm−1 (≈1439 K)
We have employed 1.3 × 109 trajectories with an appropriate Monte Carlo sampling of the initial conditions for the results reported in this Letter
Summary
The application of this method to the formation of ozone via ternary recombination reaction O2 þ O þ Ar → O3 þ Ar is based on the assumption that the internal degrees of freedom of the oxygen molecule do not play an essential role since the excitation of the O2 vibrational mode requires high collision energy over 1000 cm−1 (≈1439 K). Theoretical rate coefficients.—Figure 2 shows the rate coefficient k3ðEc; αÞ as function of collision energy obtained for different values of angle α between O2 and the direction to Ar. Comparing the upper set of data (indicated by circles), which are associated with the ozone molecules of all binding energies, and the lower set (squares), i.e., the formation rates of “deeply bound” levels of O3 with binding energies larger than 200 cm−1 (≈288 K), one can conclude that the majority of molecules formed through ternary recombination are highly excited.
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