El acceso a la versión del editor puede requerir la suscripción del recurso Access to the published version may require subscription Ultrafast Electron Dynamics in Phenylalanine Initiated by Attosecond Pulses Abstract:In the last decade attosecond technology has opened up the investigation of ultrafast electronic processes in atoms, simple molecules and solids. Here we report the application of isolated attosecond pulses to prompt ionization of the amino acid phenylalanine, and the subsequent detection of ultrafast dynamics on a sub-4.5-fs temporal scale, which is shorter than the vibrational response of the molecule. The ability to initiate and observe such electronic dynamics in polyatomic molecules represents a crucial step forward in attosecond science, which is progressively moving towards the investigation of more and more complex systems.One Sentence Summary: Ultrafast electron dynamics on a sub-4.5-fs temporal scale, which precedes any nuclear motion, is initiated in an amino acid by attosecond pulses.

We present the first direct measurement of ultrafast charge migration in a biomolecular building block – the amino acid phenylalanine. Using an extreme ultraviolet pulse of 1.5 fs duration to ionize molecules isolated in the gas phase, the location of the resulting hole was probed by a 6 fs visible/near-infrared pulse. By measuring the yield of a doubly charged ion as a function of the delay between the two pulses, the positive hole was observed to migrate to one end of the cation within 30 fs. This process is likely to originate from even faster coherent charge oscillations in the molecule being dephased by bond stretching which eventually localizes the final position of the charge. This demonstration offers a clear template for observing and controlling this phenomenon in the future.

The fast and accurate analysis of chiral chemical mixtures is crucial for many applications but remains challenging. Here we use elliptically-polarized femtosecond laser pulses at high repetition rates to photoionize chiral molecules. The 3D photoelectron angular distribution produced provides molecular fingerprints, showing a strong forward-backward asymmetry which depends sensitively on the molecular structure and degree of ellipticity. Continuously scanning the laser ellipticity and analyzing the evolution of the rich, multi-dimensional molecular signatures allows us to observe real-time changes in the chemical and chiral content present with unprecedented speed and accuracy. We measure the enantiomeric excess of a compound with an accuracy of 0.4% in 10 min acquisition time, and follow the evolution of a mixture with an accuracy of 5% with a temporal resolution of 3 s. This method is even able to distinguish isomers, which cannot be easily distinguished by mass-spectrometry.

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Attosecond pump-probe experiments performed in small molecules have allowed tracking charge dynamics in the natural time scale of electron motion. That this is also possible in biologically relevant molecules is still a matter of debate, because the large number of available nuclear degrees of freedom might destroy the coherent charge dynamics induced by the attosecond pulse. Here we investigate extreme ultraviolet-induced charge dynamics in the amino acid tryptophan. We find that, although nuclear motion and nonadiabatic effects introduce some decoherence in the moving electron wave packet, these do not significantly modify the coherence induced by the attosecond pulse during the early stages of the dynamics, at least for molecules in their equilibrium geometry. Our conclusions are based on elaborate theoretical calculations and the experimental observation of sub-4 fs dynamics, which can only be reasonably assigned to electronic motion. Hence, attosecond pump-probe spectroscopy appears as a promising approach to induce and image charge dynamics in complex molecules.