Ultrafast electron dynamics in an amino acid measured by attosecond pulses

Electron transfer within a single molecule is the fundamental step of many biological processes and chemical reactions. It plays a crucial role in catalysis, DNA damage by ionizing radiation, photosynthesis, photovoltaics, and for switches based on molecular nano-junctions. The investigation of this process has been the subject of considerable research effort [1-2]. In this work we present the first direct measurement of ultrafast charge migration in a biomolecular building block, the amino acid phenylalanine, using attosecond pulses [3]. Clean plumes of isolated, neutral molecules were produced by laser induced acoustic desorption (LIAD) technique [4]. Phenylalanine molecules were irradiated by a short train of attosecond pulses produced by high-order harmonic generation in Xenon (the train was composed by two attosecond pulses), with a photon energy in the range 16-40 eV, followed at a variable temporal delay by a 6-fs visible/near infrared (500-950 nm, VIS/NIR) probe pulse. The parent and fragment ions produced were then extracted into a linear time of flight device for mass analysis. Figures 1(a)-(b) show the mass spectra obtained individually from the XUV and VIS/NIR pulses.