Quantum Chemistry and Physical Chemistry Section
The methods of quantum mechanics are applied to the study of a wide variety of both organic and inorganic compounds. Molecular structure and properties are predicted on the basis of theoretical calculations. Due to the recent developments in computer technology, the precision of the calculation is often competitive with (and sometimes superior to) experimental measurements. Three categories of molecules are studied: 1. Transition metal compounds (complexes of Ti, Cr, Mn, Fe, Co, Ni, Cu, Rh, Pd, Pt, U...) Study of the relationship between molecular geometry and the optical, magnetic, thermodynamic, kinetic and catalytic properties. 2. Organic heterocyclic molecules with pharmaceutical potential: study of different reaction patterns (additions, substitutions, rearrangements). 3. Clusters of main-group elements: study of electron counts in relation to chemical reactivity. GAS-PHASE, ENVIRONMENTAL & SURFACE CHEMISTRY Gas-phase reactions involving free radicals are crucial in combustion chemistry, atmosphere chemistry, plasma chemistry and metal atom chemistry. Investigations of elementary reactions of relevance to these areas have been going on in the Section since more than 20 years. The research is focused toward obtaining fundamental data on the chemical reactivity of radicals, open-shell molecules and metal atoms by the direct measurement of kinetic coefficients and of product distributions, over wide temperature and pressure ranges. The principal objectives are to identify and to quantify the relations between the reactivity and the physico-chemical properties of the reactants involved. This research is also of direct pratical value, as it pertains to environmental chemistry. The combustion related research concerns the formation of the precursors of polycyclic aromatic hydrocarbon (PAH) and of soot, as well as the formation and reduction of nitrogen oxides. The present atmospheric chemistry propects are directed mainly toward tropospheric oxidation of unsatured hydrocarbons, including biogenic VOC, and their role in the formation of ambient ozone. Investigated heterogeneous processes concern interactions between radicals and mainly Si- or SiO2 surfaces, over a wide temperature range. This research relates in part semiconductor processing (colloboration with IMEC) and for another part to the characterisation of spacecraft heat-schield materials. MATRIX ISOLATION FR-IR SPECTROMETRY OF DNA-BASES. SEMICONDUCTOR GAS SENSORS Tautomerisation and H-Bond interaction of the DNA-bases uracil, cytosine, adenine and guanine are chemical phenomena with far-reaching implications in biochemical and genetic processes. In order to obtain quantitative information on these phenomena, the above DNA-bases and a series of simple model molecules are isolated in Ar ak 10K and investigated by FT-IR and FT-Ramen spectrometry. Combination with high-level ab initio calculations allows the accurate characterisation of the various tautomers and of their H-bond sites. In close collaboration with the MAP/MS division of IMEC, the fundamental processes underlying the use of SnO2 semiconductors as gas sensors, are investigated by means of various physicochemical techniques.