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Study of the formation mechanism for atmospheric ozone helps to understand development of planetary atmosphere. We focus on anomalous mass-independent isotope effect. To understand the nature of isotope effect we consider all stages of ozone formation with commonly used mechanism at the low pressure regime - energy transfer (Lindemann) mechanism which involves metastable intermediate state O3*. O3* is described by scattering resonance in quantum mechanics. Particularly, scattering resonances can be calculated using of stabilization method of Clary. Stabilization approach implies that eigenvalues change as a functions of stabilization parameter (extension of the grid boundary). Based on quantum mechanical calculations of scattering resonances, kinetic rate coefficients were computed. Found resonance states were used for calculation of kinetics rate coefficients such as equilibrium and recombination coefficients for three pressure regimes (0.3, 30 and 3000 atm). Influence of pressure was estimated as well as contributions of other kinetic parameters - stabilization constant weight of each resonance, rotational, vibrational and electronic partition functions for molecule 686 O3.
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Four Isotope-Labeled Recombination Pathways of Ozone Formation
A theoretical approach is developed for the description of all possible recombination pathways in the ozone forming reaction, without neglecting any process a priori, and without decoupling the individual pathways one from another. These pathways become physically distinct when a rare isotope of oxygen is introduced, such as 18O, which represents a sensitive probe of the ozone forming reaction. Each isotopologue of O3 contains two types of physically distinct entrance channels and two types of physically distinct product wells, creating four recombination pathways. Calculations are done for singly and doubly substituted isotopologues of ozone, eight rate coefficients total. Two pathways for the formation of asymmetric ozone isotopomer exhibit rather different rate coefficients, indicating large isotope effect driven by ΔZPE-difference. Rate coefficient for the formation of symmetric isotopomer of ozone (third pathway) is found to be in between of those two, while the rate of insertion pathway is smaller by two orders of magnitude. These trends are in good agreement with experiments, for both singly and doubly substituted ozone. The total formation rates for asymmetric isotopomers are found to be somewhat larger than those for symmetric isotopomers, but not as much as in the experiment. Overall, the distribution of lifetimes is found to be very similar for the metastable states in symmetric and asymmetric ozone isotopomers.
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- Award ID(s):
- 1920523
- PAR ID:
- 10220275
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 26
- Issue:
- 5
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 1289
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Scattering resonances above dissociation threshold are computed for four isotopically substituted ozone species: 16 O 18 O 16 O, 16 O 16 O 18 O, 18 O 16 O 18 O and 16 O 18 O 18 O, using a variational method with accurate treatment of the rotation–vibration coupling terms (Coriolis effect) for all values of the total angular momentum J from 0 to 4. To make these calculations numerically affordable, a new approach was developed which employs one vibrational basis set optimized for a typical rotational excitation ( J , Λ ), to run coupled rotation–vibration calculations at several desired values of J . In order to quantify the effect of Coriolis coupling, new data are contrasted with those computed using the symmetric-top rotor approximation, where the rotation–vibration coupling terms are neglected. It is found that, overall, the major properties of scattering resonances (such as their lifetimes, the number of these states, and their cumulative partition function Q ) are all influenced by the Coriolis effect and this influence grows as the angular momentum J is raised. However, it is found that the four isotopically substituted ozone molecules are affected roughly equally by the Coriolis coupling. When the ratio η of partition functions for asymmetric over symmetric ozone molecules is computed, the Coriolis effect largely cancels, and this cancelation seems to occur for all values of J . Therefore, it does not seem grounded to attribute any appreciable mass-independent symmetry-driven isotopic fractionation to the Coriolis coupling effect.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules26051289
