The study of chemical reactivity of isolated atoms and small metal molecules with small unsaturated molecules of catalytic interest can allow to evidence the first and intermediate steps of the relevant reaction pathway. To study these highly reactive molecules, the methods used are either jet-cooling in a rare gas supersonic expansion or isolation at cryogenic temperatures in a frozen rare gas (matrix isolation). In this case to isolate the complexes or the first intermediate species, the frozen inert rare gas solid constitutes a suitable, chemically inactive cage. The matrix plays a role of trapping cage and stabilizes (for infinite or long period of time) the interacting or highly species, as long as the conditions are maintained, in an environment close to that observed for isolated systems in the gas phase, but allowing a high detectivity and studies of long-time scale photophysical or photochemical processes.
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In parallel, Quantum chemical calculation are performed with different methods DFT, pure and hybrid or post Hartree-Fock, taking into account at a high level the electron correlation. For each system, the method reaching the best performance in terms of reproduction of observable and spectroscopic properties, as well as practicability, is selected and used to make predictions on the electronic structure and on the missing steps in the reaction pathway.
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Among the systems studied recently, one can mention those involving molecular hydrogen by transition metal atoms and group 13 dimers (such as Pd(1S) + H2(1Σg+)
-> Pd(H2) (1A1) et
Pt(3D) + H2(1Σg+)
->
PtH2(1A1), M2
+ H2 ->
M2H2,
M = Ga, In.)
Also reactions of complexation, insertion or oxidative addition with NO ou O2
(M + O2
-> M(O2) and M(O2)* ->
OMO). In both cases, the geometrical and electronic structure calculations for ground , metastable and excited states are necessary to account for the observed formation pathways.
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We have investigated cobalt oxide molecular systems of the type ConOm, with n = 1-3 and m = 2-8, the formation mechanisms, molecular structures and the electronic and vibrational spectroscopic properties. Also we are leading a program of systematic investigations on a series of M-C=O, M2
-C=O, (M being a transition metal) "model systems" to fill the gap in our knowledge on the low frequency modes and derive a correlation between spectroscopic observables and the coordination bond energies.
We are currently studying the reactions of transition metal dimers M2 (M = Ti, Co or Ni) with O2 or N2 in order to study the formation mechanism and the structures of molecular species of the type M2O2n, M2N2n, with n = 1 to 4, which can be considered elementary molecular "bricks" in the build-up of larger oxide or nitride clusters, on which materials with promising optical or semi-conducting properties. For these metals, studies point out reactivities for dimer different than for atoms and the possibility of triggering reactions in specific low energy electronic states (2 to 0.5eV). Such systems could open new possibilities in the fields of surface photochemistry or photocatalysis.
Ni(O2) synthesis
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Energetic and topological analysis of Mo and Mo2 reactivity
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Other on-going projects are for instance the conception of set-ups for reaction enthalpy measurements using micro-calorimetric methods or the spectrally- or time-resolved fluorescence in the visible to IR domain, to apply to the study of the foe-mentioned systems.
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Reactional intermediaries isolated in solid neon with a 3K Cryostat |
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A high-resolution interferometer |
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Spectroscopic markers using electronic and vibrationnal transitions for the Ti2+N2-> Ti2N2 reaction |
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Isotopic fine structure of Ni2O2 in solid neon |
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Bibliography
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 "Reactional intermediaries isolated in solid neon with a 3K Cryostat")
 "A high-resolution interferometer")
 "Spectroscopic markers using electronic and vibrationnal transitions")
 "Isotopic fine structure of Ni2O2 in solid neon")
