Charge migration induced by attosecond pulses in bio-relevant molecules (original) (raw)
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Electron localization following attosecond molecular photoionization
Nature, 2010
For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10 215 -s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale 1-4 has become possible only with the recent development of isolated attosecond (10 218 -s) laser pulses 5 . Such pulses have been used to investigate atomic photoexcitation and photoionization 6,7 and electron dynamics in solids 8 , and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H 2 and D 2 was monitored on femtosecond timescales 9 and controlled using few-cycle near-infrared laser pulses 10 . Here we report a molecular attosecond pump-probe experiment based on that work: H 2 and D 2 are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.
Control of charge migration in molecules by ultrashort laser pulses
Physical Review A, 2015
Due to electronic many-body effects, the ionization of a molecule can trigger ultrafast electron dynamics appearing as a migration of the created hole charge throughout the system. Here we propose a scheme for control of the charge migration dynamics with a single ultrashort laser pulse. We demonstrate by fully ab initio calculations on a molecule containing a chromophore and an amine moieties that simple pulses can be used for stopping the charge-migration oscillations and localizing the charge on the desired site of the system. We argue that this control may be used to predetermine the follow-up nuclear rearrangement and thus the molecular reactivity.
Journal of Modern Optics, 2016
Adiabatic attosecond charge migration (AACM) in a linear molecule or cation such as HCCI + means that the system has been prepared in a superposition state e.g. of the electronic ground and first excited states, corresponding to a surplus of density of valence electrons on one side which is compensated by a deficit of electron density on the other side. Subsequently, the surplus and deficit interchange such that the surplus of electron density migrates from its initial site to the opposite site, and back, periodically. The migration proceeds adiabatically on the attosecond time domain, i.e. without diabatic transitions between eigenstates. It is associated with electronic flux that mediates the charge migration. Here, we tailor a femtosecond π/2 laser pulse such that it induces AACM in the oriented model HCCI + , with maximum electronic flux. The case study shows that the flux is generated already during the laser pulse, suggesting equivalent processes during laser initiations of AACM in many or all other systems. The results are obtained by means of quantum dynamics simulation.
Probing Molecular Dynamics at Attosecond Resolution with Femtosecond Laser Pulses
Physical Review Letters, 2003
The kinetic energy distribution of D + ions resulting from the interaction of a femtosecond laser pulse with D2 molecules is calculated based on the rescattering model. From analyzing the molecular dynamics, it is shown that the recollision time between the ionized electron and the D + 2 ion can be read from the D + kinetic energy peaks to attosecond accuracy. We further suggest that more precise reading of the clock can be achieved by using shorter fs laser pulses (about 15fs).
Molecular Modes of Attosecond Charge Migration
Physical Review Letters, 2021
First-principles calculations are employed to elucidate the modes of attosecond charge migration (CM) in halogenated hydrocarbon chains. We use constrained density functional theory (DFT) to emulate the creation of a localized hole on the halogen and follow the subsequent dynamics via time-dependent DFT. We find low-frequency CM modes (∼1 eV) that propagate across the molecule and study their dependence on length, bond order, and halogenation. We observe that the CM speed (∼4 Å=fs) is largely independent of molecule length, but is lower for triple-bonded versus double-bonded molecules. Additionally, as the halogen mass increases, the hole travels in a more particlelike manner as it moves across the molecule. These heuristics will be useful in identifying molecules and optimal CM detection methods for future experiments, especially for halogenated hydrocarbons which are promising targets for ionization-triggered CM.
Attosecond intramolecular electron dynamics
Xviiith International Conference on Ultrafast Phenomena, 2013
We present results of numerical simulations indicating a complex laser driven electron dynamics inside simple molecular systems on the attosecond time scale. This attosecond electron dynamics influences the instant of ionization of the molecule and the final electron momentum distributions.
Applied Sciences, 2019
Electron coherence is a fundamental quantum phenomenon in today’s ultrafast physics and chemistry research. Based on attosecond pump–probe schemes, ultrafast X-ray photoelectron imaging of molecules was used to monitor the coherent electron dynamics which is created by an XUV pulse. We performed simulations on the molecular ion H 2 + by numerically solving time-dependent Schrödinger equations. It was found that the X-ray photoelectron angular and momentum distributions depend on the time delay between the XUV pump and soft X-ray probe pulses. Varying the polarization and helicity of the soft X-ray probe pulse gave rise to a modulation of the time-resolved photoelectron distributions. The present results provide a new approach for exploring ultrafast coherent electron dynamics and charge migration in reactions of molecules on the attosecond time scale.
Femtosecond Dynamics of DNA-Mediated Electron Transfer
Proceedings of The National Academy of Sciences, 1999
Diverse biophysical and biochemical studies have sought to understand electron transfer (ET) in DNA in part because of its importance to DNA damage and its repair. However, the dynamics and mechanisms of the elementary processes of ET in this medium are not fully understood and have been heavily debated. Two fundamental issues are the distance over which charge is transported and the time-scale on which the transport through the -stack of the DNA base pairs may occur. With femtosecond resolution, we report direct observation in DNA of ultrafast ET, initiated by excitation of tethered ethidium (E), the intercalated electron acceptor (A); the electron donor (D) is 7-deazaguanine (Z), a modified base, placed at different, fixed distances from A. The ultrafast ET between these reactants in DNA has been observed with time constants of 5 ps and 75 ps and was found to be essentially independent of the D-A separation (10-17 Å). However, the ET efficiency does depend on the D-A distance. The 5-ps decay corresponds to direct ET observed from 7-deazaguanine but not guanine to E. From measurements of orientation anisotropies, we conclude that the slower 75-ps process requires the reorientation of E before ET, similar to E͞nucleotide complexes in water. These results reveal the nature of ultrafast ET and its mechanism: in DNA, ET cannot be described as in proteins simply by a phenomenological parameter, . Instead, the involvement of the base pairs controls the time scale and the degree of coherent transport.
Attosecond control in photoionization of hydrogen molecules
2011
We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1s g and 2p u states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.