^{1,a)}and Reinhard Schinke

^{1,b)}

### Abstract

The recombination of ozone via the chaperon mechanism, i.e., and , is studied by means of classical trajectories and a pairwise additive potential energy surface. The recombination rate coefficient has a strong temperature dependence, which approximately can be described by with . It is negligible for temperatures above 700 K or so, but it becomes important for low temperatures. The calculations unambiguously affirm the conclusions of Hippler *et al.* [J. Chem. Phys.93, 6560 (1990)] and Luther *et al.* [Phys. Chem. Chem. Phys.7, 2764 (2005)] that the chaperon mechanism makes a sizable contribution to the recombination of at room temperature and below. The dependence of the chaperon recombination rate coefficient on the isotopomer, studied for two different isotope combinations, is only in rough qualitative agreement with the experimental data. The oxygen atom isotopeexchange reaction involving ArO and van der Waals complexes is also investigated; the weak binding of O or to Ar has only a small effect.

Financial support by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. The authors are grateful to J. Troe, K. Luther, K. Oum, and S. Yu. Grebenshchikov for stimulating discussions concerning the recombination of ozone.

I. INTRODUCTION

II. CALCULATIONS

A. Preparation of reactants

B. Definition of products

C. Rate coefficients and cross sections

III. RESULTS

A. Cross sections for reactions

B. Rate coefficients for and reactions

C. Third-order recombination rate coefficients

D. Isotope dependence of recombination rate coefficients

IV. DISCUSSION

V. CONCLUSIONS

### Key Topics

- Ozone
- 83.0
- Exchange reactions
- 17.0
- Isotopes
- 16.0
- Equilibrium constants
- 13.0
- Dissociation energies
- 12.0

## Figures

(a) Distribution of the rotational angular momentum in the vdW complex for 300 K and several delay times after the preparation of the vdW molecule. (b) Distribution of the total angular momentum of the vdW complex for 300 K and several delay times. In both figures the normalization is such that the area of the distributions is proportional to the number of molecules at a particular delay time.

(a) Distribution of the rotational angular momentum in the vdW complex for 300 K and several delay times after the preparation of the vdW molecule. (b) Distribution of the total angular momentum of the vdW complex for 300 K and several delay times. In both figures the normalization is such that the area of the distributions is proportional to the number of molecules at a particular delay time.

Internal energy distributions of the complexes formed in reactions (2c) and (2d) for several temperatures. They are determined at the end of the collisions when Ar has left the complex. Both the complexes in the main wells and in the vdW wells are taken into account.

Internal energy distributions of the complexes formed in reactions (2c) and (2d) for several temperatures. They are determined at the end of the collisions when Ar has left the complex. Both the complexes in the main wells and in the vdW wells are taken into account.

Energy and initial-state dependent cross sections for reaction (2c). is the collision energy and is the initial rotational state of . The upper (lower) panel shows the results for definition 1 (2) for the formation of a stable ozone molecule. In these calculations the ArO vdW molecule has no initial internal energy.

Energy and initial-state dependent cross sections for reaction (2c). is the collision energy and is the initial rotational state of . The upper (lower) panel shows the results for definition 1 (2) for the formation of a stable ozone molecule. In these calculations the ArO vdW molecule has no initial internal energy.

(a) Rate coefficients for the exchange reactions (16a) and (16b) as functions of temperature. For comparison, also the rate coefficient for the exchange reaction is shown. The measured rate for the latter reaction is taken from Ref. 32; because the temperature dependence for the reaction with three isotopes has not been measured, the curve shown is the average of the reaction rates for and as given in Ref. 32. The experiment covers the range from 230 to 350 K. (b) Rate coefficients and for recombination reactions (2c) and (2d), respectively, as functions of temperature. The solid (dashed) lines indicate the results for definition 1 (2) for the formation of a stable ozone molecule. The symbols indicate the temperatures at which calculations have been performed.

(a) Rate coefficients for the exchange reactions (16a) and (16b) as functions of temperature. For comparison, also the rate coefficient for the exchange reaction is shown. The measured rate for the latter reaction is taken from Ref. 32; because the temperature dependence for the reaction with three isotopes has not been measured, the curve shown is the average of the reaction rates for and as given in Ref. 32. The experiment covers the range from 230 to 350 K. (b) Rate coefficients and for recombination reactions (2c) and (2d), respectively, as functions of temperature. The solid (dashed) lines indicate the results for definition 1 (2) for the formation of a stable ozone molecule. The symbols indicate the temperatures at which calculations have been performed.

Rate coefficients and for reactions (2c) and (2d), respectively, as functions of the stabilization frequency (in ) in Eq. (9).

Rate coefficients and for reactions (2c) and (2d), respectively, as functions of the stabilization frequency (in ) in Eq. (9).

Third-order rate coefficient for definitions 1 (thick solid line) and 2 (thin solid line). Comparison with the estimation of the chaperon rate coefficient of Luther *et al.* (Ref. 28) (dashed line) and the experimental recombination rate coefficients (• • •). The experimental data are the same as in Ref. 28.

Third-order rate coefficient for definitions 1 (thick solid line) and 2 (thin solid line). Comparison with the estimation of the chaperon rate coefficient of Luther *et al.* (Ref. 28) (dashed line) and the experimental recombination rate coefficients (• • •). The experimental data are the same as in Ref. 28.

Third-order rate coefficient for different stabilization frequencies (in ). Comparison with the experimental rate coefficients (• • •).

Third-order rate coefficient for different stabilization frequencies (in ). Comparison with the experimental rate coefficients (• • •).

## Tables

Relative recombination rate coefficients for two isotope combinations and 300 K.

Relative recombination rate coefficients for two isotope combinations and 300 K.

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