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Theoretical Study of Ultrafast Electron Dynamics in Amino Acids
View the table of contents for this issue, or go to the journal homepage for more 2015 J. Phys.: Conf. Ser. 635 112129
(http://iopscience.iop.org/1742-6596/635/11/112129)
Theoretical
Study
of
Ultrafast
Electron
Dynamics
in
Amino
Acids
D. Ayuso∗1, A. Palacios∗, P. Decleva†, F. Mart´ın∗‡2∗ Departamento de Qu´ımica, M´odulo 13,Universidad Aut´onoma de Madrid, Cantoblanco 28049, Madrid, Spain † Dipartimento di Scienze Chimiche e Farmaceutiche, Universit`a di Trieste and CNR-Istituto Officina dei
Materiali, 34127 Trieste, Italy
‡ Instituto Madrile˜no de Estudios Avanzados en Nanociencia, Cantoblanco 28049 Madrid, Spain
Synopsis Prompt ionization of large biological molecules may induce ultrafast charge migration along the molec-ular skeleton, preceding any nuclear rearrangement[1,2]. This phenomenon has been recently observed in the amino acid phenylalanine [3] in a two-color pump probe experiment, where the production of ionic fragments was measured as a function of the time delay between the two pulses and charge fluctuations manifested as sub-4.5 fs oscillations in the quantum yield of a specific doubly charged fragment. We present our latest results in glycine, and compare with previous findings in phenylalanine [3]. We seek to perform a systematic study including larger aminoacids such as tryptophan.
The development of attosecond technology has enabled the real-time observation of electron motion in atoms, molecules and condensed mat-ter [4]. In the case of large biological systems, such as amino acids, sudden ionization from a molecular orbital may trigger an ultrafast elec-tronic response which is solely driven by electron correlation, as predicted in various theoretical works [1, 2]. However, due to the large band-width of attosecond pulses employed in state-of-the-art experiments [3, 4], electrons are usually removed not from one but from many orbitals, thus leading to a coherent superposition of ionic states. Therefore, an accurate description of the ionization process becomes crucial in the descrip-tion of these experimental observadescrip-tions.
We have performed a theoretical study of the field-free evolution of the electronic wave packet generated in amino acids (glycine, phenylala-nine and tryptophan) upon the interaction with with attosecond pulses. The ionization ampli-tudes have been quantitatively determined for all open channels using the static-exchange DFT method [5] developed by Decleva and collabora-tors, which makes use of the Kohn-Sham DFT to describe molecular bound states and of the Galerkin approach to evaluate continuum wave functions in the field of the corresponding Kohn-Sham density. The evolution of the electronic wave packet has then been described by using a standard time-dependent density matrix formal-ism. The results of the numerical simulations clearly show the production of an ultrafast elec-tronic response occurring in a sub-femtosecond time scale and are in good agreement with recent experimental observations [3]. We notice that, in contrast with most previous works, most valence and inner-valence electrons are efficiently ionized
and therefore the observed dynamics is that of a delocalized hole. We have further analyzed the role of the emitted electron in the hole migration mechanism and observed that even faster charge fluctuations (faster than the experimental reso-lution) might arise as a consequence of the inter-play between the ground and continuum states.
1.6 fs
3.7 fs
4.4 fs
0 fs
Figure 1. Relative variation of the hole density generated by an attosecond XUV pulse in the amino acid glycine with respect to its time-averaged value (yellow: 10−4a.u., purple: −10−4a.u.). Time is
ref-ereed to the end of the pulse. References
[1] L. S. Cederbaum et al 1999 Chem. Phys. Lett. 307, 205-210.
[2] F. Remacle et al 2006 P.N.A.S. 103, 6793-6798. [3] F. Calegari et al 2014 Science 346, 6207 336-339. [4] F. Krausz et al 2009 Rev. Mod. Phys. 81, 163. [5] M. Stener et al 2002 Chem. Phys. Lett. 351 469.
1E-mail: david.ayuso@uam.es 2
E-mail: fernando.martin@uam.es
XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015) IOP Publishing Journal of Physics: Conference Series 635 (2015) 112129 doi:10.1088/1742-6596/635/11/112129
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