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Etudes ultrarapides de la dynamique de solvatation par spectroscopie optique et X

English title Ultrafast optical and X-ray spectroscopy studies of solvation dynamics
Applicant Chergui Majed
Number 124520
Funding scheme Project funding (Div. I-III)
Research institution Laboratoire de spectroscopie ultrarapide EPFL - SB - ISIC - LSU
Institution of higher education EPF Lausanne - EPFL
Main discipline Physical Chemistry
Start/End 01.04.2009 - 31.03.2011
Approved amount 153'850.00
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All Disciplines (3)

Discipline
Physical Chemistry
Biophysics
Condensed Matter Physics

Keywords (11)

solvation dynamics; diatomics; ion-pair states; wavepacket motion; vibrational relaxation; ultrafast spectroscopy; X-ray absorption spectroscopy; electronic structure; molecular structure; ultrafast; pump-probe

Lay Summary (English)

Lead
Lay summary
Solvation dynamics represent the rearrangement of the environment around a solute whose electronic and/or molecular structure have changed. Their relevance stems from the fact that most of chemistry and biology take place in liquids, and that all chemical or biochemical reactions entail a change of electronic and molecular structure, in which the environment plays as it determines their efficiency and outcome.Atomic motions typically take place on the time scale of femtoseconds and the length scale of sub-angstroms. Many relevant processes occurring on slower timescales can only be fully understood by revealing these underlying initial events.Probing solvation dynamics in real-time requires ultrafast techniques, such as laser pump-probe spectroscopy. An electronic structure change of the solute is induced by a first pulse, bringing the solute-solvent system out of equilibrium. The evolution of the system, which is governed by the interaction of the solute with its environment, can then be followed by a second probe pulse, whose time delay with respect to the pump pulse is adjustable. The pump-probe scheme in the optical domain delivers precise temporal information, but not about the structure of the solvent shell or of the solute. For this purpose, the probe pulse has to be a hard X-ray pulse. In this project, we combine laser-only pump-probe experiments with laser pump/X-ray probe studies to elucidate relaxation pathways and the structural changes of the solute and the solvent in the process of solvation dynamics.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Associated projects

Number Title Start Funding scheme
116533 Etudes ultrarapides optique et par rayons X de la dynamique de solvatation dans l'eau et dans les alcools 01.04.2007 Project funding (Div. I-III)
105344 Etude en "temps-réel" des déformations photoinduites en phase condensée 01.10.2004 Project funding (Div. I-III)
135502 Interplay between solvation dynamics and intramolecular structural dynamics in solutions: Ultrafast optical and X-ray spectroscopic studies 01.04.2011 Project funding (Div. I-III)

Abstract

We propose to investigate the dynamics of electronic and nuclear solvation processes using a small diatomic solute (I2) in solutions. The nuclear dynamics will be studied by generating vibrational wave packets on the bound covalent B-state of the molecule, which will be probed by femtosecond transient absorption in the optical and X-ray domains. The detection of nuclear wave packets by fs X-ray absorption spectroscopy would open a new opportunity to investigate vibrational relaxation and non-adiabatic dynamics by the direct observation of evolving molecular structures, in any class of medium. Electronic solvation dynamics will be studied by exciting the ion-pair states of I2, which leads to formation of a giant dipole. The ultrafast kinetics of these states will be characterized optically by 2-photon excited femtosecond fluorescence up-conversion and, structurally by picosecond and femtosecond X-ray absorption spectroscopy. The ion-pair states of I2 offer a case study to disentangle the intra- from intermolecular contributions to solvation dynamics, and to investigate the response of the solvent to an oscillating dipole. In general, the study of small molecule dynamics by fs X-ray absorption spectroscopy will provide benchmarks for future X-ray experiments on more complex systems.
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