MOLCOTUV · Molecular control with tailored UV pulses
FP6 — Marie Curie Actions (Human Resources and Mobility)
- Duration
- 2007-10-15 → 2009-10-14
- EU contribution
- €215,156
- Participants
- 1
- Scheme
- EIF
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Results in brief
Final Activity and Management Report Summary - MOLCOTUV (Molecular control with tailored UV pulses)
The advent of the Velocity Map Imaging has revolutionised the experimental approaches used in the molecular dynamics studies as it offers a multiplex detection method, which provides exceptional energy resolution alongside with simultaneous measurements of the angular distributions. Ever since its introduction in the late 1990s, this powerful technique has underpinned significant advances in our understanding of atomic and molecular processes and it has been applied to numerous studies of fundamental dynamical processes: bimolecular collisions, photodissociation and photoionisation. In combination with time resolved measurements, the ion and photoelectron imaging sheds light onto the pathways followed by the molecules from the entrance to the exit channel. Imaging with femtosecond resolution produces the 'movie' of the molecular transformation by giving real time information on the electronic and nuclear wave-packet motions, electronic dephasing, and photoionisation and photodissociation dynamics. We took advantage of the great potential of the imaging method for the study of complex and fast dynamics. In particular, we have studied two benchmark systems: CH3I and NO2. For the former, we have measured the photionisation and the predissociation of CH3I (6s) B(2E) Rydberg state initiated around 200 nm. Very importantly, we have shown for the first time that it is possible to investigate in real time molecular alignment effects by using broadband fs pulse: we have measured the rotational angular moment alignment of CH3 fragment. As for NO2, we have studied competing multiphoton and multichannel dynamics induced with femtosecond pulses of 400 and 266 nm. With these experiments we tried to establish the origin of a very intriguing oscillatory dynamics induced by 400 nm pulses. For the time being and in spite of efforts from several groups, these oscillations elude an unambiguous explanation. In the recent years, high order harmonic generation (HHG) spectroscopy has emerged as a new tool for probing molecular structures and dynamics, including subfemtosecond arrangements of nuclei and electrons. This technique consists of measuring the spectrum of the coherent radiation emitted by molecules subjected to intense laser fields. It has been shown both theoretically and experimentally that the yield of high harmonic generation is strongly modified when the molecules are spatially aligned. By improving the degree of alignment of the molecular axis and we could reveal new features in the HHG spectra of CO2 and N2 associated to new mechanisms responsible for HHG and the interference of some nonadiabatic dynamics of the ion in the laser field.
Data: CORDIS, © European Union
Project objective
The project aims at developing a coherent control scheme in the perturbative interaction regime by using a phase and amplitude shaped UV pump pulses and at exploiting them as a new spectroscopic tool. Pulse shaping consists in changing the Gaussian amplitude profile of femtosecond pulses by modifying both the phase relationships between the frequencies that make up the pulse and their relative amplitudes.Shaping of ultrafast pulses enabled the active control of physicochemical processes. We propose the implementation of coherent control methods in small systems to steer the outcome of chemical reactions from electronically excited states. This will be realized in gas phase reactions by femtosecond shaped pulses pump-probe spectroscopy involving velocity map imaging for the photoelectron/photoion detection.Gas phase experiments provide the standard for the evaluation of high level ab-initio calculations. A change in the time-resolved signal by the application of a frequency sweep across the pump pulse may elucidate the vibronic couplings governing the molecular dynamics. With theoretical support, we can access to information relating to the critical parameters of these transition barriers.Our goal is to control the outcome of a unimolecular reaction by taking advantage of the phase of the electromagnetic field and the quantum-mechanical phase of the polyatomic molecule. To circumvent the dynamical complexity, we will implement experimentally an adaptive feedback control. As the pulse shaper comprises a very large number of pixels, finding the solution to achieve the desired control is a very time consuming process.We propose a different approach where a phase mask is defined by a mathematical function with a minimum number of control parameters. Then physical effects such as linear and quadratic chirp, pulse duration are maintained, making the problem easier to analyse in order to elucidate the relaxation dynamics and to further propose rational solutions.
Original text from CORDIS.
Participants
- UNIVERSITE PAUL SABATIER - TOULOUSE 3 · TOULOUSECoordinatorCity levelFrance
Links
Data: CORDIS, © European Union