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36 results on '"Xiong, Yanwei"'

1. Monitoring the evolution of relative product populations at early times during a photochemical reaction

Author

Nunes, Joao Pedro Figueira, Ibele, Lea Maria, Pathak, Shashank, Attar, Andrew R., Bhattacharyya, Surjendu, Boll, Rebecca, Borne, Kurtis, Centurion, Martin, Erk, Benjamin, Lin, Ming-Fu, Forbes, Ruaridh J. G., Goff, Nate, Hansen, Christopher S., Hoffmann, Matthias, Holland, David M. P., Ingle, Rebecca A., Luo, Duan, Muvva, Sri Bhavya, Reid, Alex, Rouzée, Arnaud, Rudenko, Artem, Saha, Sajib Kumar, Shen, Xiaozhe, Venkatachalam, Anbu Selvam, Wang, Xijie, Ware, Matt R., Weathersby, Stephen P., Wilkin, Kyle, Wolf, Thomas J. A., Xiong, Yanwei, Yang, Jie, Ashfold, Michael N. R., Rolles, Daniel, and Curchod, Basile F. E.

Subjects
Physics - Chemical Physics
Abstract

Identifying multiple rival reaction products and transient species formed during ultrafast photochemical reactions and determining their time-evolving relative populations are key steps towards understanding and predicting photochemical outcomes. Yet, most contemporary ultrafast studies struggle with clearly identifying and quantifying competing molecular structures/species amongst the emerging reaction products. Here, we show that mega-electronvolt ultrafast electron diffraction in combination with ab initio molecular dynamics calculations offer a powerful route to determining time-resolved populations of the various isomeric products formed after UV (266 nm) excitation of the five-membered heterocyclic molecule 2(5H)-thiophenone. This strategy provides experimental validation of the predicted high (~50%) yield of an episulfide isomer containing a strained 3-membered ring within ~1 ps of photoexcitation and highlights the rapidity of interconversion between the rival highly vibrationally excited photoproducts in their ground electronic state.

Published
2023
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2. Quantum state tomography of molecules by ultrafast diffraction

Author

Zhang, Ming, Zhang, Shuqiao, Xiong, Yanwei, Zhang, Hankai, Ischenko, Anatoly A., Vendrell, Oriol, Dong, Xiaolong, Mu, Xiangxu, Centurion, Martin, Xu, Haitan, Miller, R. J. Dwayne, and Li, Zheng

Subjects
Quantum Physics, Physics - Chemical Physics
Abstract

Ultrafast electron diffraction and time-resolved serial crystallography are the basis of the ongoing revolution in capturing at the atomic level of detail the structural dynamics of molecules. However, most experiments employ the classical "ball-and-stick" depictions, and the information of molecular quantum states, such as the density matrix, is missing. Here, we introduce a framework for the preparation and ultrafast coherent diffraction from rotational wave packets of molecules, and we establish a new variant of quantum state tomography for ultrafast electron diffraction to characterize the molecular quantum states. The ability to reconstruct the density matrix of molecules of arbitrary degrees of freedom will provide us with an unprecedentedly clear view of the quantum states of molecules, and enable the visualization of effects dictated by the quantum dynamics of molecules., Comment: arXiv admin note: substantial text overlap with arXiv:2012.11899

Published
2021
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6. Monitoring the Evolution of Relative Product Populations at Early Times during a Photochemical Reaction

Author

Figueira Nunes, Joao Pedro, primary, Ibele, Lea Maria, additional, Pathak, Shashank, additional, Attar, Andrew R., additional, Bhattacharyya, Surjendu, additional, Boll, Rebecca, additional, Borne, Kurtis, additional, Centurion, Martin, additional, Erk, Benjamin, additional, Lin, Ming-Fu, additional, Forbes, Ruaridh J. G., additional, Goff, Nathan, additional, Hansen, Christopher S., additional, Hoffmann, Matthias, additional, Holland, David M. P., additional, Ingle, Rebecca A., additional, Luo, Duan, additional, Muvva, Sri Bhavya, additional, Reid, Alexander H., additional, Rouzée, Arnaud, additional, Rudenko, Artem, additional, Saha, Sajib Kumar, additional, Shen, Xiaozhe, additional, Venkatachalam, Anbu Selvam, additional, Wang, Xijie, additional, Ware, Matt R., additional, Weathersby, Stephen P., additional, Wilkin, Kyle, additional, Wolf, Thomas J. A., additional, Xiong, Yanwei, additional, Yang, Jie, additional, Ashfold, Michael N. R., additional, Rolles, Daniel, additional, and Curchod, Basile F. E., additional

Published
2024
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9. Ultrafast electron diffraction instrument for gas and condensed matter samples

Author

Wang, Yibo, Saha, Sajib Kumar, Li, Tianlin, Xiong, Yanwei, Wilkin, Kyle, Adhikari, Anil, Loes, Michael, Abourahma, Jehad, Hong, Xia, Adenwalla, S., Sinitskii, Alexander, Centurion, Martin, Wang, Yibo, Saha, Sajib Kumar, Li, Tianlin, Xiong, Yanwei, Wilkin, Kyle, Adhikari, Anil, Loes, Michael, Abourahma, Jehad, Hong, Xia, Adenwalla, S., Sinitskii, Alexander, and Centurion, Martin

Abstract

We report the modification of a gas phase ultrafast electron diffraction (UED) instrument that enables experiments with both gas and condensed matter targets, where a time-resolved experiment with sub-picosecond resolution is demonstrated with solid state samples. The instrument relies on a hybrid DC-RF acceleration structure to deliver femtosecond electron pulses on the target, which is synchronized with femtosecond laser pulses. The laser pulses and electron pulses are used to excite the sample and to probe the structural dynamics, respectively. The new system is added with capabilities to perform transmission UED on thin solid samples. It allows for cooling samples to cryogenic temperatures and to carry out time-resolved measurements. We tested the cooling capability by recording diffraction patterns of temperature dependent charge density waves in 1T-TaS2. The time-resolved capability is experimentally verified by capturing the dynamics in photoexcited single-crystal gold.

Published
2023

17. Ultrafast electron diffraction from transiently aligned asymmetric top molecules: Rotational dynamics and structure retrieval

Author

Wilkin, Kyle, Xiong, Yanwei, Zhao, Haoran, Muvva, Sri Bhavya, Saha, S. K., Centurion, Martin, Wilkin, Kyle, Xiong, Yanwei, Zhao, Haoran, Muvva, Sri Bhavya, Saha, S. K., and Centurion, Martin

Abstract

Ultrafast electron diffraction (UED) from aligned molecules in the gas phase has successfully retrieved structures of both linear and symmetric top molecules. Alignment of asymmetric tops has been recorded with UED but no structural information was retrieved. We present here the extraction of two-dimensional structural information from simple transformations of experimental diffraction patterns of aligned molecules as a proof-of-principle for the recovery of the full structure. We align 4-fluorobenzotrifluoride with a linearly polarized laser and show that we can distinguish between atomic pairs with equal distances that are parallel and perpendicular to the aligned axis. We additionally show with numerical simulations that by cooling the molecules to a rotational temperature of 1 K, more distances and angles can be resolved through direct transformations.

Published
2022

18. Retrieval of the molecular orientation distribution from atom-pair angular distributions

Author

Xiong, Yanwei, Wilkin, Kyle J., Saha, S. K., Muvva, Sri Bhavya, Zhao, Haoran, Centurion, Martin, Xiong, Yanwei, Wilkin, Kyle J., Saha, S. K., Muvva, Sri Bhavya, Zhao, Haoran, and Centurion, Martin

Abstract

Imaging laser-induced rotational dynamics is an important and active field due to its applications in capturing reactions in the molecular frame and in molecular imaging. Experimental measurement of the molecular orientation distribution, as a function of the Euler angles, has been demonstrated for special cases when the detectable signal is generated along the molecular symmetry axis. Here we developed the general theory that maps the probability density distribution of the molecular orientation to the atom-pair angular distributions for nonlinear molecules. With the theory, the molecular orientation distribution can be retrieved from the measured atom-pair angular distribution, which we demonstrate experimentally using ultrafast electron diffractive imaging of impulsively aligned trifluoro-iodomethane molecules. The retrieved molecular orientation distribution is in good agreement with direct numerical simulations of the time-dependent Schrödinger equation using the experimental conditions. Unlike the existing retrieval methods, the retrieval method does not require solving the Schrödinger equation, works for any alignment method, and is in principle applicable to asymmetric top molecules.

Published
2022

24. Quantum state tomography of molecules by ultrafast diffraction

Author

Zhang, Ming, primary, Zhang, Shuqiao, additional, Xiong, Yanwei, additional, Zhang, Hankai, additional, Ischenko, Anatoly A., additional, Vendrell, Oriol, additional, Dong, Xiaolong, additional, Mu, Xiangxu, additional, Centurion, Martin, additional, Xu, Haitan, additional, Miller, R. J. Dwayne, additional, and Li, Zheng, additional

Published
2021
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25. Strong-field induced fragmentation and isomerization of toluene probed by ultrafast femtosecond electron diffraction and mass spectrometry

Author

Xiong, Yanwei, primary, Borne, Kurtis, additional, Carrascosa, Andrés Moreno, additional, Saha, Sajib Kumar, additional, Wilkin, Kyle J., additional, Yang, Mengqi, additional, Bhattacharyya, Surjendu, additional, Chen, Keyu, additional, Du, Wenpeng, additional, Ma, Lingyu, additional, Marshall, Nathan, additional, Nunes, J. Pedro F., additional, Pathak, Shashank, additional, Phelps, Zane, additional, Xu, Xuan, additional, Yong, Haiwang, additional, Lopata, Kenneth, additional, Weber, Peter M., additional, Rudenko, Artem, additional, Rolles, Daniel, additional, and Centurion, Martin, additional

Published
2021
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28. Compressed sensing based multi-rate sub-Nyquist sampling system

Author

Xiong Yanwei, Zhang Ping, and Zhang Jianhua

Subjects
Computer Networks and Communications, Computer science, Analog signal, Compressed sensing, Sampling (signal processing), Undersampling, Control theory, Signal Processing, Hardware_INTEGRATEDCIRCUITS, Electronic engineering, Nyquist–Shannon sampling theorem, Oversampling, Nyquist rate, Nyquist frequency, Information Systems
Abstract

Signal sampling is a vital component in modern information technology. As the signal bandwidth becomes wider, the sampling rate of analog-to-digital conversion (ADC) based on Shannon-Nyquist theorem is more and more high and may be beyond its capacity. However the analog to information converter (AIC) based on compressed sensing (CS) is designed to sample the analog signals at a sub-Nyquist sampling rate. A new multi-rate sub-Nyquist sampling (MSS) system was proposed in this article, it has one mixer, one integrator and several parallel ADCs with different sampling rates. Simulation shows the signals can be reconstructed in high probability even though the sampling rate is much lower than the Nyquist sampling rate.

Published
2015
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30. Diffractive Imaging of Laser Induced Molecular Reactions with Kiloelectron-Volt Ultrafast Electron Diffraction

Author

Xiong, Yanwei

Subjects
ultrafast electron diffraction, molecular movie, laser induced molecular alignment, molecular orientation distribution, photodissociation, Atomic, Molecular and Optical Physics, Optics, Physical Chemistry, Quantum Physics
Abstract

Capturing the structural changes during a molecular reaction with ultrafast electron diffraction (UED) requires a high spatiotemporal resolution and sufficiently high signal-to-noise to record the signals with high fidelity. In this dissertation, I have focused on the development of a tabletop gas phase keV-UED setup with a femtosecond temporal resolution. A DC electron gun was employed to generate electron pulses with a high repetition rate of 5 kHz. The space charge effect in the electron pulse was ameliorated by compressing the 90 keV electron pulse longitudinally with a time varying electric field in an RF cavity. The velocity mismatch between electron and laser pulses was mitigated using a tilted laser pulse with an incident angle such that longitudinal component of the laser velocity is matched to the speed of electron pulse. The combination of these two techniques enabled the setup to reach a temporal resolution of 240 fs, more recently ~200 fs, and a timing drift of 50 fs rms over several hours. The UED was used to capture the laser induced alignment of linear and nonlinear molecules. The high beam current and femtosecond resolution allowed us to extract the molecular orientation distribution (MOD) of the molecular ensemble with high fidelity as it evolved from the prompt alignment to the past multiple revivals. To retrieve the MOD of nonlinear molecules, I developed a theory that maps the MOD to the atom-pair angular distributions. The retrieval method does not require solving Schrödinger equation and works for any alignment methods. We also investigated ionization, fragmentation and isomerization of toluene generated by an IR strong laser field. Combined with the time-of-flight mass spectrometry, UED can determine the structure and yield of cations. A comparison of measurements to scattering calculations shows that scattering computation with independent atom model is inadequate to describe electron scattering from cations, and ab-initio calculation is required. Finally, the molecular photodissociation experiments with CF3I and iodobenzene induced by a UV pulse were demonstrated with the keV-UED. Advisor: Martin Centurion

Published
2023

36. Ultrafast structural dynamics of UV photoexcited cis , cis -1,3-cyclooctadiene observed with time-resolved electron diffraction.

Author

Muvva SB, Liu Y, Chakraborty P, Nunes JPF, Attar AR, Bhattacharyya S, Borne K, Champenois EG, Goff N, Hegazy K, Hoffmann MC, Ji F, Lin MF, Luo D, Ma L, Odate A, Pathak S, Rolles D, Rudenko A, Saha SK, Shen X, Wang X, Ware MR, Weathersby S, Weber PM, Wilkin KJ, Wolf TJA, Xiong Y, Xu X, Yang J, Matsika S, Weinacht T, and Centurion M

Abstract

Conjugated diene molecules are highly reactive upon photoexcitation and can relax through multiple reaction channels that depend on the position of the double bonds and the degree of molecular rigidity. Understanding the photoinduced dynamics of these molecules is crucial for establishing general rules governing the relaxation and product formation. Here, we investigate the femtosecond time-resolved photoinduced excited-state structural dynamics of cis , cis -1,3-cyclooctadiene, a large-flexible cyclic conjugated diene molecule, upon excitation with 200 nm using mega-electron-volt ultrafast electron diffraction and trajectory surface hopping dynamics simulations. We tracked the photoinduced structural changes from the Franck-Condon region through the conical intersection seam to the ground state. Our findings revealed a novel primary reaction coordinate involving ring distortion, where the ring stretches along one axis and compresses along the perpendicular axis. The nuclear wavepacket remains compact along this reaction coordinate until it reaches the conical intersection seam, and it rapidly spreads as it approaches the ground state, where multiple products are formed.

Published
2024
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