XVIth International Workshop on
Quantum Systems in
Chemistry and Physics
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Quantum calculations on transient species in physics and chemistry
Najia Komiha
LCTM- University Mohamed V-Agdal
Rabat Morocco
Informations on transient species are often necessary to explain formation, dissociation or spectroscopic properties of molecules. The quantum chemistry method used should be able to discribe these species. The case of transition states in organic chemistry is presented here. As an example, The reactional mechanism of the 1,3 dipolar cycloaddition of a cyclic nitrone on a substituted enoate is studied using the DFT method.This method take into account a aprt of the correlation energy and gives qualitative results . Structures of eight possible cyclo-adducts and transition states are determined. Relative rates , stereo and regioselectivity is analysed and discussed.
The excited electronic states are also transient species of great spectroscopic interest .S2O is a molecule of atmospheric medium.Its formation (or dissociation) at low energy is studied here. The Potential Energy Surfaces (PES) of all states correlating to the lowest asymptote are mapped using the highly correlated method MRCI+Q. The spin-orbit coupling is taken into account. One dimensional cuts of the three-dimensional potential energy surfaces are presented for linear and bent geometries. Anisotropy in regard of the different approaches is shown and the S-SO one seem to be favored.
A study of the sulfur chromophors are then presented and electronic excited states responsible of color of S3-, S4-, S4+ determined The PES and some spectroscopic constants of the lowest states of S3- are mapped using The SA-CASSCF and CCSD(T) accurate methods.

References

1) ‘Theoretical study of the mechanism of the 1,3-dipolar cycloaddition reaction of methyl-3-fluoro-3-trifluoromethyl prop-2-Enoate with Pyrroline-1-Oxyde’
K. Marakchi, H. Abou El Makarim, O. K. Kabbaj, N. Komiha
Phys. Chem. News 52 (2010) 128-136
2) ‘On the formation of S2O at low energies: An Ab-Initio study’
Isabelle Navizet, Najia Komiha , Roberto Linguerri, Gilberte Chambaud and Pavel Rosmus
Chemical Physics Letters, Volume 500, Issues 4-6, 19 November 2010, Pages 207-210
3) ‘Electronic states of the Ultramarine chromophore S3-‘
R.Linguerri,N.Komiha,J.Fabian,P.Rosmus
Z.Phys.chem.,222(1),2008,163-176






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