On stabilization of scattering resonances in recombination reaction that forms ozone

Abstract

Calculations of energy transfer in the recombination reaction that forms ozone are carried out within the framework of the mixed quantum/classical theory and using the dimensionally reduced 2D-model of ozone molecule, with bending motion neglected. Recombination rate coefficients are obtained at room temperature for symmetric and asymmetric isotopomers of singly and doubly substituted isotopologues. The processes of resonance formation, spontaneous decay, collisional dissociation, and stabilization by bath gas (Ar) are all characterized and taken into account within the steady-state approximation for kinetics. The focus is on stabilization step, where the mysterious isotopic η-effect was thought to originate from. Our results indicate no difference in cross sections for stabilization of scattering resonances in symmetric and asymmetric isotopomers. As practical results, the general and simple analytic models for stabilization and dissociation cross sections are presented, which can be applied to resonances in any ozone molecule, symmetric or asymmetric, singly or doubly substituted. Present calculations show some isotope effect that looks similar to the experimentally observed η-effect, and the origin of this phenomenon is in the rates of formation/decay of scattering resonances, determined by their widths, that are somewhat larger in asymmetric isotopomers than in their symmetric analogues. However, the approximate two-dimensional model used here is insufficient for consistent and reliable description of all features of the isotopic effect in ozone. Calculations using an accurate 3D model are still needed. Published by AIP Publishing. [http://dx

Recombination reactions as a possible mechanism of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth

“…It should be stressed that this expression leads to δ = 0 in the limit of k′ = k ′ s , which means that in the case of ozone, where recombination stops at O 3 and does not go further (no O 4 or O 8 are formed at normal conditions), the only possible source of large isotopic enrichment is η-effect, k′ > k ′ s . In the case of sulfur the ratio k′=k ′ s is not known, and it is too early to speculate about its value since the origin of η-effect is not yet entirely clear, even in the case of ozone (20,21). If the analogy with ozone is valid, this value would be on the order of 133‰.…”

“…We build upon our experience (18)(19)(20)(21) with the recombination reaction that forms ozone, O + O 2 → O 3 , and is known to produce significant mass-independent fractionation of oxygen isotopes 17 O and 18 O in today's atmosphere of Earth (22)(23)(24) and in many laboratory experiments (25,26). In ozone formation two features essential for the isotope effect are (25) fast atomexchange processes that reshuffle isotopes in the mixture (e.g., 18 O).…”

A full-dimensional model of ozone forming reaction: the absolute value of the recombination rate coefficient, its pressure and temperature dependencies

“…17 Those calculations gave detailed insight into the recombination process 20,21 and, also, allowed us to derive a simple analytical formula for the description of energy-transfer in ozone. 22 The only serious limitation of our previous work was the dimensionally reduced approximation for O3*. Indeed, if excitation of the bending mode is not allowed, then the total number of vibrational accessed by following the link in the citation at the bottom of the page.…”

“…22 In principle, the experimental recombination rate can be recovered by an ad hoc adjustment (e.g., based on statistical argument of the density of states, as we did in ref. 21), but it is certainly desirable to develop a complete treatment of ozone recombination, including all degrees of freedom.…”

“…Using a method that employs hyper-spherical coordinates, the sequential diagonalization-truncation technique, and complex absorbing potential 23 we compute energies and lifetimes of scattering resonances in a full-dimensional model of ozone (including its bending motion) for a broad range of rotational excitations, up to J = 64, Ka ≤ J. This information, together with the analytic formula for collisional energy-transfer and collision-induced dissociation derived earlier, 22 permits building a more complete version of the energy-transfer mechanism of ozone recombination. When complemented by contribution of the chaperon mechanism (as suggested by Troe 3 ) our results agree well with experimental data, including the absolute value of the recombination rate coefficient, its temperature and pressure dependencies.…”