Orateur
Prof.
Sergy Yu. Grebenshchikov
(Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen)
Description
The three-body recombination reaction,
O_2 + O + M --> O_3 + M (1)
is one of the central reactions of the Chapman cycle controlling the stability of the stratospheric ozone (O_3) layer. This reaction, in which O_3 is initially formed at dissociation threshold, is also responsible for large enrichments of heavy isotopomers of ozone. The enrichments, which seem unrelated to the natural abundances of oxygen isotopes and therefore are called “surprising”, are observed both in the field measurements and in the lab [1]. Despite numerous studies in the past few years, the isotope fractionations are still far from being satisfactorily explained and several essential questions remain to be solved [2].
In this talk I plan to discuss recent quantum mechanical studies of two unusual isotope dependences in reaction (1):
Isotope Effect 1(IE-1), the dependence of the recombination rate on the difference of zero-point energies of the two fragmentation channels to which excited ozone can dissociate, i.e. X + YZ --> XYZ*-->XY + Z, where X, Y, and Z stand for the three isotopes of oxygen;
Isotope Effect 2 (IE-2), the symmetry dependence of the recombination rate: the rate is smaller for symmetric molecules (e.g. XYX) than for non-symmetric ones (e.g. XXY).
Both isotope effects, IE-1 and IE-2, will be analyzed using the full-blown quantum mechanical calculations of near-threshold resonance spectra as well as the cross-sections for collisional stabilization of ozone at dissociation threshold. It will be shown that the distributions of resonance widths in the rotating molecule and the peculiar topology of ozone interaction potential are able to explain most of the observed isotope dependences.
[1] K. Mauersberger et al., Advances in Atomic, Molecular, and Optical Physics 50, 1 (2005).
[2] R. Schinke, S. Yu.Grebenshchikov, M. V. Ivanov, and P. Fleurat-Lessard, Annu. Rev. Phys. Chem. 57, 625 (2006).
Auteur principal
Prof.
Sergy Yu. Grebenshchikov
(Max-Planck-Institut für Dynamik und Selbstorganisation, Göttingen)
