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PhD subjects

2 sujets IRAMIS

Dernière mise à jour : 19-04-2018


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• Atomic and molecular physics

 

Electronic dynamics of bio-relevant systems: toward a modeling of the deactivation processes of excited states

SL-DRF-18-0674

Research field : Atomic and molecular physics
Location :

Service Laboratoire Interactions, Dynamique et Lasers (LIDyL)

(SBM)

Saclay

Contact :

Valérie BRENNER

Starting date : 01-10-2018

Contact :

Valérie BRENNER

CEA - DRF/IRAMIS/LIDyL/SBM

01.69.08.37.88

Thesis supervisor :

Valérie BRENNER

CEA - DRF/IRAMIS/LIDyL/SBM

01.69.08.37.88

Personal web page : http://iramis.cea.fr/Pisp/valerie.brenner/

Laboratory link : http://iramis.cea.fr/LIDyL/SBM/

Many complex molecular systems absorbing light in the near UV spectral range, including those of paramount biological importance, like DNA bases or proteins, are endowed with mechanisms of excited-state deactivation following UV absorption. These mechanisms are of major importance for the photochemical stability of these species since they provide them a rapid and efficient way to dissipate the electronic energy in excess into vibration, thus avoiding photochemical processes to take place and then structural damages which affect the biological function of the system. In this context, the study of gas phase bio-relevant systems such peptides as proteins building blocks should lead to better understanding the photophysical phenomena involved in the relaxation mechanisms of life components. The size of the systems, their flexibility, the existence of non-covalent interactions which governs structures and the nature of the excited states require the use of sophisticated theoretical models in order to characterize the preferentially formed conformations in gas phase as well as to investigate the electronic deactivation mechanisms of the first excited states.



The focus of the PhD project concerns the implementation of a computational strategy to both characterize the first excited states and simulate their potential energy surfaces in order to determine the relaxation pathways. This theoretical research project contains then the development, evaluation and validation of modern quantum chemical methods dedicated to excited states. It will be backed up by key gas phase experiments performed in our group on bio-relevant systems using recent spectroscopic techniques which provide precise data on their spectroscopic properties and their electronic dynamics of relaxation.



Moreover, it will take place in the context of the following of the ANR project, ESBODYR or «Excited States of BiO-relevant systems: towards ultrafast conformational Dynamics with Resolution» (Coord V. Brenner, 2014-2018) and will benefit from an access to the national High Performance Computing resources (GENCI: TGCC/ IDRIS / CINES).

Electronic dynamics of bio-relevant systems: a synergetic experimental and theoretical approach

SL-DRF-18-0678

Research field : Atomic and molecular physics
Location :

Service Laboratoire Interactions, Dynamique et Lasers (LIDyL)

(SBM)

Saclay

Contact :

Michel MONS

Valérie BRENNER

Starting date : 01-10-2018

Contact :

Michel MONS

CEA - DRF/IRAMIS/LIDyL/SBM

01 69 08 20 01

Thesis supervisor :

Valérie BRENNER

CEA - DRF/IRAMIS/LIDyL/SBM

01.69.08.37.88

Personal web page : http://iramis.cea.fr/Pisp/valerie.brenner/

Laboratory link : http://iramis.cea.fr/LIDyL/SBM/

More : http://iramis.cea.fr/Pisp/michel.mons/

Many complex molecular systems absorbing light in the near UV spectral range, including those of paramount biological importance, like DNA bases or proteins, are endowed with mechanisms of excited-state deactivation following UV absorption. These mechanisms are of major importance for the photochemical stability of these species since they provide them a rapid and efficient way to dissipate the electronic energy in excess into vibrations, thus avoiding photochemical processes to take place and then structural damages which affect the biological function of the system. In this context, the study of gas phase bio-relevant systems such peptides as proteins building blocks should lead to a better understanding of the photophysical phenomena involved in the relaxation mechanisms of life components. This Ph. D project aims at both investigating the electronic dynamics of bio-relevant model systems, i.e. building block of life components, and documenting the basic phenomena controlling the lifetime of the excited states, through a dual approach using most recent methodological tools, consisting of:



i) An experimental characterization of i) the lifetimes, in nano-, pico- and femtosecond pump-probe experiments, and ii) the nature of the electronic states formed. Sophisticated diagnostic techniques, such as a photo-electron velocity map imaging diagnosis, will be used. These experiments will allow us to identify the relaxation pathways followed by the system, and in particular to assess the role of the several excited states together with the effect of its environment.

ii) A theoretical modeling of the processes involved, in particular to assess the role of specific regions of the potential energy surface (PES), namely the conical intersections, and to determine the motions that trigger deactivation. The systems’ size, their flexibility, the non-covalent interactions, which govern the structures, and the nature of the excited states require the implementation of a computational strategy using sophisticated quantum chemical methods dedicated to excited states (non-adiabatic dynamic, coupled cluster method and multireference configuration interaction method) in order to characterize the first excited states, simulate their PES and eventually determine the relaxation pathways.



Moreover, this work will take place in the following of the ANR project, ESBODYR, for «Excited States of BiO-relevant systems: towards ultrafast conformational Dynamics with Resolution» (Coord V. Brenner, 2014-2018). Finally, the theoretical part will benefit from an access to the national High Performance Computing resources (GENCI: TGCC/ IDRIS / CINES) as well as from access to both the femtosecond SLIC server of IRAMIS (Saclay) and the Laser Center of the University Paris-Sud (CLUPS).

 

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