Description du projet
Explorer la dynamique structurelle des réactions chimiques
Lors des réactions chimiques, les distances séparant les molécules deviennent si faibles que les liaisons chimiques entre les atomes sont rompues et que de nouvelles liaisons se forment. Les configurations apparaissant au cours de cette transformation chimique, qui ne correspondent ni à des réactifs ni à des produits, sont appelées «états de transition». Le projet c-TSD-p, financé par l’UE, entend surmonter les obstacles qui entravent la représentation expérimentale des transformations structurelles survenant pendant cet état de transition. L’équipe mettra au point une configuration qui devrait permettre d’initier la réaction chimique à un moment précis à l’aide d’une impulsion laser femtoseconde. La longueur d’onde accordable de l’impulsion laser devrait permettre aux chercheurs de contrôler la vitesse à laquelle les deux composés participant à la réaction entrent en contact. La structure 3D de l’état de transition sera observée grâce à l’imagerie par explosion coulombienne.
Objectif
For bonds to be broken and new bonds to be formed, chemical reactants have to come close to each other and evolve through transient intermediate configurations known as the transition state. Transition state dynamics is closely related to reaction mechanisms and of fundamental importance in chemistry. Much work has been done to unravel these dynamics, which often involve major structural rearrangement of atoms. However, there are a lot of open questions since to date none of the applied spectroscopic techniques has directly delivered the time-dependent transition state structure. I propose to develop a novel probe that images, one molecule at a time, the full three-dimensional atomic configuration of individual transition states as they evolve: Reaction precursors are prepared using molecular ions and small (ionic) clusters with defined initial structure and tunable internal temperature. Starting from these well-defined initial configurations, chemical dynamics will be initiated by a femtosecond laser pulse. Timed Coulomb Explosion Imaging, induced by extremely short intense laser or X-ray pulses together with full coincidence momentum imaging of all fragments is then applied as a probe. The latter yields the evolving transition state structure by mapping the position of all atoms as a function of time-delay between the two pulses. I argue that the progress in laser technology in recent years was imperative to make such a scheme feasible now, since it allows measurements at high repetition rate, which is absolutely crucial. I propose work packages of increasing complexity to study ground state chemical reactions in the presence of solvent molecules and under the influence of a control pulse. The structural information obtained from Coulomb Explosion Imaging gives direct insight into how reaction mechanisms change under such conditions. I anticipate that light will be shed on some of the long-standing open questions surrounding transition state dynamics.
Champ scientifique
Programme(s)
Régime de financement
ERC-COG - Consolidator GrantInstitution d’accueil
34125 Kassel
Allemagne