Pengju Zhang

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Zhang

First Name

Pengju

ORCID

0000-0001-7746-2113

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Publications 1 - 10 of 17

Attosecond spectroscopy of molecular charge transfer uncovers a 1.5-fs delay in population transfer
Matselyukh, Danylo T.; Rott, Florian; Schnappinger, Thomas; et al. (2025)
Nature Communications
The transfer of population between two intersecting quantum states is the most fundamental event in many dynamical processes in physics, chemistry, biology, and material science. Any two-state description of such processes requires population leaving one state to instantaneously appear in the other. We show that coupling to additional states, present in all real-world systems, can cause a measurable delay in population transfer. Using attosecond spectroscopy supported by quantum-chemical calculations, we measure a delay of 1.46 ± 0.41 fs at a charge-transfer crossing in CF3I+, where an electron hole moves from the fluorine atoms to iodine. Our measurements also resolve the other fundamental quantum-dynamical processes involved in the charge-transfer reaction: a vibrational rearrangement time of 9.38 ± 0.21 fs (during which the vibrational wave packet travels to the state crossing) and a population-transfer time of 2.3–2.4 fs. Our work shows that delays in population transfer readily appear in otherwise-adiabatic reactions and predicts them to be on the order of a single-femtosecond for molecular valence-state crossings. These results have implications for many research areas, such as atomic and molecular physics, charge transfer, or light harvesting.
Reconstruction of attosecond pulses in the presence of interfering dressing fields using a 100 kHz laser system at ELI-ALPS
Hammerland, Daniel; Zhang, Pengju; Kühn, Sergei; et al. (2019)
Journal of Physics B: Atomic, Molecular and Optical Physics
Attosecond Pulse Trains (APT) generated by high-harmonic generation (HHG) of high-intensity near-infrared (IR) laser pulses have proven valuable for studying the electronic dynamics of atomic and molecular species. However, the high intensities required for high-photon-energy, high-flux HHG usually limit the class of adequate laser systems to repetition rates below 10 kHz. Here, APT's generated from the 100 kHz, 160 W, 40 fs laser system (HR-1) currently under commissioning at the extreme light infrastructure attosecond light pulse source (ELI-ALPS) are reconstructed using the reconstruction of attosecond beating by interference of two-photon Transitions (RABBIT) technique. These experiments constitute the first attosecond time-resolved photoelectron spectroscopy measurements with attosecond pulses performed at 100 kHz repetition rate and one of the first experiments performed at ELI-ALPS in the framework of projects commissioning its newly installed technologies. These RABBIT measurements were taken with an additional IR field temporally locked to the extreme-ultraviolet APT, resulting in an atypical ω beating. We show that the phase of the 2ω beating recorded under these conditions is strictly identical to that observed in standard RABBIT measurements within second-order perturbation theory. This work highlights an experimental simplification for future experiments based on attosecond interferometry (or RABBIT), which is particularly useful when lasers with high average powers are used.
Resolving the phase of Fano resonance wave packets with photoelectron frequency-resolved optical gating
Zhang, Pengju; Liang, Hao; Han, Meng; et al. (2025)
Nature Photonics
The creation of structured electronic wave packets (EWPs) energetically close to Fano resonances has been achieved with ultrafast extreme ultraviolet coherent light sources. However, direct real-time observations of EWP evolution and full reconstructions of the quantum properties of EWPs, including both amplitude and phase, are lacking. Here we introduce and demonstrate a comprehensive approach for the direct measurement and complete characterization of structured EWPs created within a prototypical Fano resonance. Because of its analogy with frequency-resolved optical gating (FROG), we named the method photoelectron FROG. The correlated EWP is initiated by a carefully engineered extreme UV pump pulse. A weak near-infrared laser field, serving as a probe pulse, samples the evolution of the EWPs in the time domain, as well as in the frequency domain. The amplitude and phase of the EWPs are obtained via a time-dependent reconstruction algorithm based on a short-time Fourier transformation. Given the excellent agreement between our experimental results and time-dependent reconstructions, we expect this method to be broadly applicable to the study of ultrafast processes, especially electronic ones, in complex systems, as well as the coherent control of such systems on their fundamental timescales.
Ionization Energy of Liquid Water Revisited
Perry, Conaill F.; Zhang, Pengju; Nunes, Fernanda B.; et al. (2020)
The Journal of Physical Chemistry Letters
Enhanced damage induced by secondary high-energy electrons
Yan, S.; Zhu, Xiaolong; Zhang, Shaofeng; et al. (2020)
Physical Review A
A new kind of radiotherapy scheme based on the resonant Auger-interatomic Coulombic decay mechanism (RA ICD) was proposed in the work of Gokhberg et al. [Nature 505, 661 (2014)], which may effectively reduce the overall radiation dose in traditional x-ray radiotherapy. An electron produced in this scheme carries most of the energy of the primary x-ray photon. Through the present experiment using an energetic electron impact on a NeAr dimer, we demonstrate that three processes, namely, the interatomic Coulombic decay triggered by a Ne 2s electron ionization, ICD triggered by Ar+* (3p(4)nl >= 5d), and charge transfer in the Ar2+ Ne ion, can take place and enhance the yields of slow electrons and ions. Therefore, energetic secondary electrons make the x-ray RA ICD scheme more toxic in radiotherapy.
Direct Observation of Anionic Yields from the Liquid–Vapor Interface by Electron Irradiation
Chen, Ziwei; Li, Ziyuan; Xie, Jingchen; et al. (2024)
The Journal of Physical Chemistry Letters
Dissociative electron attachment (DEA) is widely believed to play a high-profile role in ionizing radiation damages of bioorganic molecules, and its fundamentals are mainly learned from the gas-phase studies. However, the DEA process in aqueous solution is still in debate. Here we provide experimental evidence about the DEA processes of liquid methanol by using electron-impact-time-delayed mass spectrometry. In contrast to the gas- and solid-phase DEAs, methoxide ion CH3O− is the predominant product from the liquid interface. Furthermore, this anion can be produced with both the primary low-energy electrons and the inelastically scattered and secondary low-energy electrons. On the contrary, the primary low-energy electrons in the liquid bulk are more likely to be solvated, rather than directly participating in the DEA process. Our study provides new insights into radiation chemistry, particularly of bioorganic relevance.
Low-energy electron distributions from the photoionization of liquid water: a sensitive test of electron mean free paths
Gadeyne, Titouan; Zhang, Pengju; Schild, Axel; et al. (2022)
Chemical Science
The availability of accurate mean free paths for slow electrons (<50 eV) in water is central to the understanding of many electron-driven processes in aqueous solutions, but their determination poses major challenges to experiment and theory alike. Here, we describe a joint experimental and theoretical study demonstrating a novel approach for testing, and, in the future, refining such mean free paths. We report the development of Monte-Carlo electron-trajectory simulations including elastic and inelastic electron scattering, as well as energy loss and secondary-electron production to predict complete photoelectron spectra of liquid water. These simulations are compared to a new set of photoelectron spectra of a liquid-water microjet recorded over a broad range of photon energies in the extreme ultraviolet (20–57 eV). Several previously published sets of scattering parameters are investigated, providing direct and intuitive insights on how they influence the shape of the low-energy electron spectra. A pronounced sensitivity to the escape barrier is also demonstrated. These simulations considerably advance our understanding of the origin of the prominent low-energy electron distributions in photoelectron spectra of liquid water and clarify the influence of scattering parameters and the escape barrier on their shape. They moreover describe the reshaping and displacement of low-energy photoelectron bands caused by vibrationally inelastic scattering. Our work provides a quantitative basis for the interpretation of the complete photoelectron spectra of liquids and opens the path to fully predictive simulations of low-energy scattering in liquid water.
Observation of intermolecular Coulombic decay in liquid water
Zhang, Pengju; Perry, Conaill; Luu, Tran; et al. (2020)
OSA Technical Digest ~ International Conference on Ultrafast Phenomena 2020
Intermolecular Coulombic decay has been observed in liquid water for the first time. This was achieved using monochromatized high-harmonic radiation coupled to a liquid microjet and an electron-electron coincidence spectrometer.
Correction: Low-energy electron distributions from the photoionization of liquid water: a sensitive test of electron mean free paths
Gadeyne, Titouan; Zhang, Pengju; Schild, Axel; et al. (2025)
Chemical Science
Bond-length dependence of attosecond ionization delays in O$_{2}$ arising from electron correlation to a shape resonance
Hammerland, Daniel; Berglitsch, Thomas; Zhang, Pengju; et al. (2024)
Science Advances
We experimentally and theoretically demonstrate that electron correlation can cause the bond-length sensitivity of a shape resonance to induce an unexpected vibrational state–dependent ionization delay in a nonresonant channel. This discovery was enabled by a high-resolution attosecond-interferometry experiment based on a 400-nm driving and dressing wavelength. The short-wavelength driver results in a 6.2–electron volt separation between harmonics, markedly reducing the spectral overlap in the measured interferogram. We demonstrate the promise of this method on O2, a system characterized by broad vibrational progressions and a dense photoelectron spectrum. We measure a 40-attosecond variation of the photoionization delays over the X2Πg vibrational progression. Multichannel calculations show that this variation originates from a strong bond-length dependence of the energetic position of a shape resonance in the b4Σg− channel, which translates to the observed effects through electron correlation. The unprecedented energy resolution and delay accuracies demonstrate the promise of visible-light–driven molecular attosecond interferometry.

Publications 1 - 10 of 17

Pengju Zhang

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