Electronic Quantum Coherence in Glycine Molecules Probed with Ultrashort X-ray Pulses in Real Time

Structural changes in nature and technology are driven by charge carrier motion. A process such as charge-directed reactivity that can be operational in radiobiology is more efficient, if energy transfer and charge motion proceeds along well-defined quantum mechanical pathways keeping the coherence and minimizing dissipation. The open question is: do long-lived electronic quantum coherences exist in complex molecules? Here, we use x-rays to create and monitor electronic wave packets in the amino acid glycine. The outgoing photoelectron wave leaves behind a positive charge formed by a superposition of quantum mechanical eigenstates. Delayed x-ray pulses track the induced electronic coherence through the photoelectron emission from the sequential double photoionization processes. The observed sinusoidal modulation of the detected electron yield as a function of time clearly demonstrates that electronic quantum coherence is preserved for at least 25 femtoseconds in this molecule of biological relevance. The surviving coherence is detected via the dominant sequential double ionization channel, which is found to exhibit a phase shift as a function of the photoelectron energy. The experimental results agree with advanced ab-initio simulations.Comment: 54 pages, 11 figure

Aufbau eines hocheffizienten Photoelektron-Photoion-Koinzidenzexperiments

This thesis describes the design, setup and characterization of a highly efficient photoelectron-photoion-coincidence-spectrometer together with first experiments. The spectrometer consists of a combination of a short ion-Time-of-Flightspectrometer and an electron-Time-of-Flight-spectrometer with a magnetic bottle for highly efficient electron detection and is adapted to the needs of the P04-beamline at the storage ring PETRA III at the Deutsches Elektronen-Synchrotron (DESY). This combination allows highly efficient coincidence measurements of decay processes of atomic and molecular samples as a result of photoexcitation and -ionization. Simulation tools for construction and measurements for the characterization of the single parts are presented. The coincidence-spectrometer itself was characterized with regard to efficiency, mass resolution (262 au) and energy resolution (up to DE/E = 3,1 %). Experiments on the electronic photoionization dynamics of Xenon after 3d-innershell excitation have been performed. At photon energies in the range of 670,25 eV - 920,25 eV a shift of the auger electron signal depending on the charge state and a double excitation of Xe5+- and Xe6+-ions at photon energies of 744,25 eV have been observed. In addition the branching ratio for the different charge states have been determined. Examinations on Nitrous Oxide verified the so-called NACHT-effect in the electronic signal, where the quadrupole moment of the oxygen 1s->3p*-resonance has an ionizing effect on the innershell electrons of the neighboring Nitrogen atoms depending on the distance with respect to the Oxygen atom. At photon energies of 539 eV the branching ratio for the fragments of CO2 has been determined. In addition signs for the synthesis of O2-molecules and an intensity distribution in the coincidence signal have been observed, which can be explained by molecular vibrations. Furthermore the use of the spectrometer for time-resolved measurements at the P04-beamline is described. This thesis closes with an outlook including suggestions for instrumental optimization and motivations for future measurements

Inner-shell X-ray absorption spectra of the cationic series NHy+(y=0–3)\mathrm{NH_y^+ ( y = 0–3)}

Ion yields following X-ray absorption of the cationic series $\mathrm{NH_y^+ ( y = 0–3)}$ were measured to identify the characteristic absorption resonances in the energy range of the atomic nitrogen K-edge. Significant changes in the position of the absorption resonances were observed depending on the number of hydrogen atoms bound to the central nitrogen atom. Configuration interaction (CI) calculations were performed to obtain line assignments in the frame of molecular group theory. To validate the calculations, our assignment for the atomic cation N$^+$, measured as a reference, was compared with published theoretical and experimental data

Electronic Quantum Coherence in Glycine Molecules Probed with Ultrashort X-ray Pulses in Real Time

Quantum coherence between electronic states of a photoionized molecule and the resulting process of ultrafast electron-hole migration have been put forward as a possible quantum mechanism of charge-directed reactivity governing the photoionization-induced molecular decomposition. Attosecond experiments based on the indirect (fragment ion-based) characterization of the proposed electronic phenomena suggest that the photoionization-induced electronic coherence can survive for tens of femtoseconds, while some theoretical studies predict much faster decay of the coherence due to the quantum uncertainty in the nuclear positions and the nuclear-motion effects. The open questions are: do long-lived electronic quantum coherences exist in complex molecules and can they be probed directly, i.e. via electronic observables? Here, we use x-rays both to create and to directly probe quantum coherence in the photoionized amino acid glycine. The outgoing photoelectron wave leaves behind a positively charged ion that is in a coherent superposition of quantum mechanical eigenstates lying within the ionizing pulse spectral bandwidth. Delayed x-ray pulses track the induced coherence through resonant x-ray absorption that induces Auger decay and by the photoelectron emission from sequential double photoionization. Sinusoidal temporal modulation of the detected signal at early times (0 - 25 fs) is observed in both measurements. Advanced ab initio many-electron simulations, taking into account the quantum uncertainty in the nuclear positions, allow us to explain the first 25 fs of the detected coherent quantum evolution in terms of the electronic coherence