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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.

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