Speaker
Description
Context: Molecular oxygen is peculiar of Earth’s atmosphere and the precursor of stratospheric ozone which absorbs most of the Sun UV radiations. Oxygen isotopic analysis allows one to trace back the origin of elements constituting Solar system primitive materials, like meteorites and comets. O$_2$ and O$_3$ formed from $^{16}$O isotope are dominant, thereby giving a reference for any process involving oxygen. A strong enrichment, about 10% greater than that following usual fractionation rules, of O$_3$ in both $^{18}$O and $^{17}$O, the so-called mass-independent fractionation (MIF), has first been observed decades ago in primitive chondrites and stratosphere [1,2], and since reproduced in laboratory experiments [3]. However, its proper quantum mechanical explanation has never been attained. Ozone is the stabilized form of the oxygen exchange reaction O + O$_2$ $\to$ O$_3^*$ $\to$ O$_2$ + O intermediate O$_3^*$. The study of the latter with $^{17}$O-enriched isotopomers of O$_2$ is thus important for a full understanding of heavy O$_3$ formation. The $^{34}$O$_2$ species has already been investigated in collision with He [4], in the context of buffer gas cooling and subsequent magnetic trapping allowed by its $S=1$ electronic spin. Furthermore, the nonzero nuclear spin of $^{17}$O, $I=5/2$, makes it a suitable candidate for further study at ultra-low temperatures, in the presence of a magnetic field.
Methodology: We have used a high quality ab initio potential energy surface [5] to perform computationally intensive full quantum investigation of the dynamics of this scattering process.
Results: We shall present cross sections and rate constants [6,7,8] for the $^{17}$O + $^{32}$O$_2$,
$^{16}$O + op$^{34}$O$_2$ and $^{17}$O + op$^{34}$O$_2$ reactions. We will discuss observed isotope effects, and the importance of symmetry in relation to nuclear spin and ortho-para conversions [8].
References:
[1] R. N. Clayton, L. Grossman, L. K. Mayeda ‘A component of primitive nuclear composition in carbonaceous meteorites’ Science 182 (1973) 485
[2] K. Mauersberger ‘Measurement of heavy ozone in the stratosphere’ GRL 8 (1981) 935-937
[3] M. H. Thiemens, J. E. Heidenreich, III ‘The mass-independent fractionation of oxygen: a novel isotope effect and its possible cosmochemical implications’ Science 219 (1983) 1073-1075
[4] J. Bohn ‘Cold collisions of O$_2$ with He’ PRA 62 (2000) 032701
[5] R. Dawes, P. Lolur, A. Li, B. Jiang, H. Guo ‘Communication : An accurate global potential energy surface for the ground electronic state of ozone’ JCP 139 (2013) 201103
[6] G. Guillon, P. Honvault, ‘Quantum dynamics of the $^{17}$O + $^{32}$O2 collision process’ JPCA 120 (2016) 8254
[7] G. Guillon, P. Honvault, ‘Quantum dynamics of $^{16}$O in collision with otho- and para-$^{17}$O$^{17}$O’ CPL 689 (2017) 62
[8] G. Guillon, M. Lepers, P. Honvault ‘Quantum dynamics of $^{17}$O in collision with otho- and para-$^{17}$O$^{17}$O’ PRA 102 (2020) 012810
| Affiliation de l'auteur principal | Lab. ICB UMR6303 CNRS/Université de Bourgogne |
|---|
