Pub Date : 2021-06-23eCollection Date: 2021-05-01DOI: 10.1063/4.0000109
Valentin Chardonnet, Marcel Hennes, Romain Jarrier, Renaud Delaunay, Nicolas Jaouen, Marion Kuhlmann, Nagitha Ekanayake, Cyril Léveillé, Clemens von Korff Schmising, Daniel Schick, Kelvin Yao, Xuan Liu, Gheorghe S Chiuzbăian, Jan Lüning, Boris Vodungbo, Emmanuelle Jal
During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump-probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm ( ), we were able to probe close to the Fe L3 edge ( ) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization.
在过去二十年里,人们开发了多种模型来解释飞秒光激发后磁化的超快淬灭。这些模型可分为两大类,分别依赖于角动量的局部或非局部转移。利用时间分辨 X 射线共振磁反射率获取飞秒分辨率的磁深度剖面图,可以区分局部效应和非局部效应。在此,我们利用 FLASH2 自由电子激光器(FEL)上的定制反射仪,在泵浦探针几何中演示了这一技术的可行性。虽然FLASH2仅限于产生基本波长为4纳米(≃ 310 eV)的光子,但我们能够利用FEL的三次谐波探测磁性薄膜的铁L 3边缘(706.8 eV)。我们的方法使我们能够提取结构和磁不对称信号,揭示出不同时间尺度上的两种动态,它们支撑着非均质磁化损失和磁层厚度 2 Å 的显著扩张,随后是振荡。未来对数据的分析将为结合飞秒和纳米分辨率对瞬态磁深度剖面进行全面定量描述铺平道路,这将为深入了解超快退磁的微观机制提供更多信息。
{"title":"Toward ultrafast magnetic depth profiling using time-resolved x-ray resonant magnetic reflectivity.","authors":"Valentin Chardonnet, Marcel Hennes, Romain Jarrier, Renaud Delaunay, Nicolas Jaouen, Marion Kuhlmann, Nagitha Ekanayake, Cyril Léveillé, Clemens von Korff Schmising, Daniel Schick, Kelvin Yao, Xuan Liu, Gheorghe S Chiuzbăian, Jan Lüning, Boris Vodungbo, Emmanuelle Jal","doi":"10.1063/4.0000109","DOIUrl":"10.1063/4.0000109","url":null,"abstract":"<p><p>During the last two decades, a variety of models have been developed to explain the ultrafast quenching of magnetization following femtosecond optical excitation. These models can be classified into two broad categories, relying either on a local or a non-local transfer of angular momentum. The acquisition of the magnetic depth profiles with femtosecond resolution, using time-resolved x-ray resonant magnetic reflectivity, can distinguish local and non-local effects. Here, we demonstrate the feasibility of this technique in a pump-probe geometry using a custom-built reflectometer at the FLASH2 free-electron laser (FEL). Although FLASH2 is limited to the production of photons with a fundamental wavelength of 4 nm ( <math><mrow><mo>≃</mo> <mn>310</mn> <mo> </mo> <mtext>eV</mtext></mrow> </math> ), we were able to probe close to the Fe <i>L</i> <sub>3</sub> edge ( <math><mrow><mn>706.8</mn> <mo> </mo> <mtext>eV</mtext></mrow> </math> ) of a magnetic thin film employing the third harmonic of the FEL. Our approach allows us to extract structural and magnetic asymmetry signals revealing two dynamics on different time scales which underpin a non-homogeneous loss of magnetization and a significant dilation of 2 Å of the layer thickness followed by oscillations. Future analysis of the data will pave the way to a full quantitative description of the transient magnetic depth profile combining femtosecond with nanometer resolution, which will provide further insight into the microscopic mechanisms underlying ultrafast demagnetization.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-06-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8225393/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39163008","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-06-18eCollection Date: 2021-05-01DOI: 10.1063/4.0000079
N Bach, S Schäfer
Ultrafast structural probing has greatly enhanced our understanding of the coupling of atomic motion to electronic and phononic degrees-of-freedom in quasi-bulk materials. In bi- and multilayer model systems, additionally, spatially inhomogeneous relaxation channels are accessible, often governed by pronounced interfacial couplings and local excitations in confined geometries. Here, we systematically explore the key dependencies of the low-frequency acoustic phonon spectrum in an elastically mismatched metal/semiconductor bilayer system optically excited by femtosecond laser pulses. We track the spatiotemporal strain wave propagation in the heterostructure employing a discrete numerical linear chain simulation and access acoustic wave reflections and interfacial couplings with a phonon mode description based on a continuum mechanics model. Due to the interplay of elastic properties and mass densities of the two materials, acoustic resonance frequencies of the heterostructure significantly differ from breathing modes in monolayer films. For large acoustic mismatch, the spatial localization of phonon eigenmodes is derived from analytical approximations and can be interpreted as harmonic oscillations in decoupled mechanical resonators.
{"title":"Ultrafast strain propagation and acoustic resonances in nanoscale bilayer systems.","authors":"N Bach, S Schäfer","doi":"10.1063/4.0000079","DOIUrl":"10.1063/4.0000079","url":null,"abstract":"<p><p>Ultrafast structural probing has greatly enhanced our understanding of the coupling of atomic motion to electronic and phononic degrees-of-freedom in quasi-bulk materials. In bi- and multilayer model systems, additionally, spatially inhomogeneous relaxation channels are accessible, often governed by pronounced interfacial couplings and local excitations in confined geometries. Here, we systematically explore the key dependencies of the low-frequency acoustic phonon spectrum in an elastically mismatched metal/semiconductor bilayer system optically excited by femtosecond laser pulses. We track the spatiotemporal strain wave propagation in the heterostructure employing a discrete numerical linear chain simulation and access acoustic wave reflections and interfacial couplings with a phonon mode description based on a continuum mechanics model. Due to the interplay of elastic properties and mass densities of the two materials, acoustic resonance frequencies of the heterostructure significantly differ from breathing modes in monolayer films. For large acoustic mismatch, the spatial localization of phonon eigenmodes is derived from analytical approximations and can be interpreted as harmonic oscillations in decoupled mechanical resonators.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8214470/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39025628","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-06-18eCollection Date: 2021-05-01DOI: 10.1063/4.0000104
Antonio Caretta, Simone Laterza, Valentina Bonanni, Rudi Sergo, Carlo Dri, Giuseppe Cautero, Fabio Galassi, Matteo Zamolo, Alberto Simoncig, Marco Zangrando, Alessandro Gessini, Simone Dal Zilio, Roberto Flammini, Paolo Moras, Alexander Demidovich, Miltcho Danailov, Fulvio Parmigiani, Marco Malvestuto
Here, we report on the conceptual design, the hardware realization, and the first experimental results of a novel and compact x-ray polarimeter capable of a single-pulse linear polarization angle detection in the extreme ultraviolet photon energy range. The polarimeter is tested by performing time resolved pump-probe experiments on a Ni80Fe20 Permalloy film at the M2,3 Ni edge at an externally seeded free-electron laser source. Comparison with similar experiments reported in the literature shows the advantages of our approach also in view of future experiments.
{"title":"A novel free-electron laser single-pulse Wollaston polarimeter for magneto-dynamical studies.","authors":"Antonio Caretta, Simone Laterza, Valentina Bonanni, Rudi Sergo, Carlo Dri, Giuseppe Cautero, Fabio Galassi, Matteo Zamolo, Alberto Simoncig, Marco Zangrando, Alessandro Gessini, Simone Dal Zilio, Roberto Flammini, Paolo Moras, Alexander Demidovich, Miltcho Danailov, Fulvio Parmigiani, Marco Malvestuto","doi":"10.1063/4.0000104","DOIUrl":"https://doi.org/10.1063/4.0000104","url":null,"abstract":"<p><p>Here, we report on the conceptual design, the hardware realization, and the first experimental results of a novel and compact x-ray polarimeter capable of a single-pulse linear polarization angle detection in the extreme ultraviolet photon energy range. The polarimeter is tested by performing time resolved pump-probe experiments on a Ni<sub>80</sub>Fe<sub>20</sub> Permalloy film at the M<sub>2,3</sub> Ni edge at an externally seeded free-electron laser source. Comparison with similar experiments reported in the literature shows the advantages of our approach also in view of future experiments.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1063/4.0000104","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39025629","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-06-15eCollection Date: 2021-05-01DOI: 10.1063/4.0000102
Florian Rott, Maurizio Reduzzi, Thomas Schnappinger, Yuki Kobayashi, Kristina F Chang, Henry Timmers, Daniel M Neumark, Regina de Vivie-Riedle, Stephen R Leone
Attosecond extreme ultraviolet (XUV) and soft x-ray sources provide powerful new tools for studying ultrafast molecular dynamics with atomic, state, and charge specificity. In this report, we employ attosecond transient absorption spectroscopy (ATAS) to follow strong-field-initiated dynamics in vinyl bromide. Probing the Br M edge allows one to assess the competing processes in neutral and ionized molecular species. Using ab initio non-adiabatic molecular dynamics, we simulate the neutral and cationic dynamics resulting from the interaction of the molecule with the strong field. Based on the dynamics results, the corresponding time-dependent XUV transient absorption spectra are calculated by applying high-level multi-reference methods. The state-resolved analysis obtained through the simulated dynamics and related spectral contributions enables a detailed and quantitative comparison with the experimental data. The main outcome of the interaction with the strong field is unambiguously the population of the first three cationic states, D1, D2, and D3. The first two show exclusively vibrational dynamics while the D3 state is characterized by an ultrafast dissociation of the molecule via C-Br bond rupture within 100 fs in 50% of the analyzed trajectories. The combination of the three simulated ionic transient absorption spectra is in excellent agreement with the experimental results. This work establishes ATAS in combination with high-level multi-reference simulations as a spectroscopic technique capable of resolving coupled non-adiabatic electronic-nuclear dynamics in photoexcited molecules with sub-femtosecond resolution.
{"title":"Ultrafast strong-field dissociation of vinyl bromide: An attosecond transient absorption spectroscopy and non-adiabatic molecular dynamics study.","authors":"Florian Rott, Maurizio Reduzzi, Thomas Schnappinger, Yuki Kobayashi, Kristina F Chang, Henry Timmers, Daniel M Neumark, Regina de Vivie-Riedle, Stephen R Leone","doi":"10.1063/4.0000102","DOIUrl":"https://doi.org/10.1063/4.0000102","url":null,"abstract":"<p><p>Attosecond extreme ultraviolet (XUV) and soft x-ray sources provide powerful new tools for studying ultrafast molecular dynamics with atomic, state, and charge specificity. In this report, we employ attosecond transient absorption spectroscopy (ATAS) to follow strong-field-initiated dynamics in vinyl bromide. Probing the Br M edge allows one to assess the competing processes in neutral and ionized molecular species. Using <i>ab initio</i> non-adiabatic molecular dynamics, we simulate the neutral and cationic dynamics resulting from the interaction of the molecule with the strong field. Based on the dynamics results, the corresponding time-dependent XUV transient absorption spectra are calculated by applying high-level multi-reference methods. The state-resolved analysis obtained through the simulated dynamics and related spectral contributions enables a detailed and quantitative comparison with the experimental data. The main outcome of the interaction with the strong field is unambiguously the population of the first three cationic states, <i>D</i> <sub>1</sub>, <i>D</i> <sub>2</sub>, and <i>D</i> <sub>3</sub>. The first two show exclusively vibrational dynamics while the <i>D</i> <sub>3</sub> state is characterized by an ultrafast dissociation of the molecule via C-Br bond rupture within 100 fs in 50% of the analyzed trajectories. The combination of the three simulated ionic transient absorption spectra is in excellent agreement with the experimental results. This work establishes ATAS in combination with high-level multi-reference simulations as a spectroscopic technique capable of resolving coupled non-adiabatic electronic-nuclear dynamics in photoexcited molecules with sub-femtosecond resolution.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-06-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1063/4.0000102","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39025627","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-06-09eCollection Date: 2021-05-01DOI: 10.1063/4.0000107
Naoya Kurahashi, Stephan Thürmer, Suet Yi Liu, Yo-Ichi Yamamoto, Shutaro Karashima, Atanu Bhattacharya, Yoshihiro Ogi, Takuya Horio, Toshinori Suzuki
We describe a magnetic bottle time-of-flight electron spectrometer designed for time-resolved photoemission spectroscopy of a liquid microjet using extreme UV and X-ray radiation. The spectrometer can be easily reconfigured depending on experimental requirements and the energy range of interest. To improve the energy resolution at high electron kinetic energy, a retarding potential can be applied either via a stack of electrodes or retarding mesh grids, and a flight-tube extension can be attached to increase the flight time. A gated electron detector was developed to reject intense parasitic signal from light scattered off the surface of the cylindrically shaped liquid microjet. This detector features a two-stage multiplication with a microchannel plate plus a fast-response scintillator followed by an image-intensified photon detector. The performance of the spectrometer was tested at SPring-8 and SACLA, and time-resolved photoelectron spectra were measured for an ultrafast charge transfer to solvent reaction in an aqueous NaI solution with a 200 nm UV pump pulses from a table-top ultrafast laser and the 5.5 keV hard X-ray probe pulses from SACLA.
{"title":"Design and characterization of a magnetic bottle electron spectrometer for time-resolved extreme UV and X-ray photoemission spectroscopy of liquid microjets.","authors":"Naoya Kurahashi, Stephan Thürmer, Suet Yi Liu, Yo-Ichi Yamamoto, Shutaro Karashima, Atanu Bhattacharya, Yoshihiro Ogi, Takuya Horio, Toshinori Suzuki","doi":"10.1063/4.0000107","DOIUrl":"https://doi.org/10.1063/4.0000107","url":null,"abstract":"<p><p>We describe a magnetic bottle time-of-flight electron spectrometer designed for time-resolved photoemission spectroscopy of a liquid microjet using extreme UV and X-ray radiation. The spectrometer can be easily reconfigured depending on experimental requirements and the energy range of interest. To improve the energy resolution at high electron kinetic energy, a retarding potential can be applied either via a stack of electrodes or retarding mesh grids, and a flight-tube extension can be attached to increase the flight time. A gated electron detector was developed to reject intense parasitic signal from light scattered off the surface of the cylindrically shaped liquid microjet. This detector features a two-stage multiplication with a microchannel plate plus a fast-response scintillator followed by an image-intensified photon detector. The performance of the spectrometer was tested at SPring-8 and SACLA, and time-resolved photoelectron spectra were measured for an ultrafast charge transfer to solvent reaction in an aqueous NaI solution with a 200 nm UV pump pulses from a table-top ultrafast laser and the 5.5 keV hard X-ray probe pulses from SACLA.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-06-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1063/4.0000107","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39235491","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-27eCollection Date: 2021-05-01DOI: 10.1063/4.0000095
Xueli Jia, Yonggang Yang, Hongsheng Zhai, Qingqing Zhang, Yuanyuan He, Yang Liu, Yufang Liu
The mechanisms of 2-(Benzo[d]thiazol-2-yl)phenol-based bifunctional probe (HBT-FS) for detecting fluoride (F-) and sulfite (SO32-) based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) have been theoretically studied. Laplacian bond order of HBT-FS indicates that the F- ion cleaves the Si-O bond and then forms Compound 2 possessing a six-membered ring with a hydrogen bond. Potential energy curves and dynamic simulations confirm that ESIPT in Compound 2 occurs along with this hydrogen bond and forms a keto structure with an emission at 623 nm, which agrees with the observed experimental value (634 nm) after adding F-. Therefore, the fluorescence red-shift (from 498 to 634 nm) of HBT-FS observed in experiment after adding F- is caused by ESIPT. The SO32- ion is added to the C5 site of HBT-FS, which is confirmed by orbital-weighted dual descriptor, and then forms Compound 3 with fluorescence located at 404 nm. The experimentally measured fluorescence at 371 nm after adding SO32- is assigned to Compound 3. Charge transfer analyses indicate that the ICT extent of Compound 3 is relatively weak compared with that of HBT-FS because of the destruction of the conjugated structure by the addition reaction of SO32-, which induces the blue-shift of the fluorescence of HBT-FS from 498 to 371 nm. The different fluorescence responses make HBT-FS a fluorescent probe to discriminatorily detect F- and SO32-.
{"title":"The mechanisms of a bifunctional fluorescent probe for detecting fluoride and sulfite based on excited-state intramolecular proton transfer and intramolecular charge transfer.","authors":"Xueli Jia, Yonggang Yang, Hongsheng Zhai, Qingqing Zhang, Yuanyuan He, Yang Liu, Yufang Liu","doi":"10.1063/4.0000095","DOIUrl":"https://doi.org/10.1063/4.0000095","url":null,"abstract":"<p><p>The mechanisms of 2-(Benzo[d]thiazol-2-yl)phenol-based bifunctional probe (HBT-FS) for detecting fluoride (F<sup>-</sup>) and sulfite (SO<sub>3</sub> <sup>2-</sup>) based on excited-state intramolecular proton transfer (ESIPT) and intramolecular charge transfer (ICT) have been theoretically studied. Laplacian bond order of HBT-FS indicates that the F<sup>-</sup> ion cleaves the Si-O bond and then forms Compound 2 possessing a six-membered ring with a hydrogen bond. Potential energy curves and dynamic simulations confirm that ESIPT in Compound 2 occurs along with this hydrogen bond and forms a keto structure with an emission at 623 nm, which agrees with the observed experimental value (634 nm) after adding F<sup>-</sup>. Therefore, the fluorescence red-shift (from 498 to 634 nm) of HBT-FS observed in experiment after adding F<sup>-</sup> is caused by ESIPT. The SO<sub>3</sub> <sup>2-</sup> ion is added to the C<sub>5</sub> site of HBT-FS, which is confirmed by orbital-weighted dual descriptor, and then forms Compound 3 with fluorescence located at 404 nm. The experimentally measured fluorescence at 371 nm after adding SO<sub>3</sub> <sup>2-</sup> is assigned to Compound 3. Charge transfer analyses indicate that the ICT extent of Compound 3 is relatively weak compared with that of HBT-FS because of the destruction of the conjugated structure by the addition reaction of SO<sub>3</sub> <sup>2-</sup>, which induces the blue-shift of the fluorescence of HBT-FS from 498 to 371 nm. The different fluorescence responses make HBT-FS a fluorescent probe to discriminatorily detect F<sup>-</sup> and SO<sub>3</sub> <sup>2-</sup>.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1063/4.0000095","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39055570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-12eCollection Date: 2021-05-01DOI: 10.1063/4.0000076
Yashoj Shakya, Ludger Inhester, Caroline Arnold, Ralph Welsch, Robin Santra
Investigating the early dynamics of chemical systems following ionization is essential for our understanding of radiation damage. However, experimental as well as theoretical investigations are very challenging due to the complex nature of these processes. Time-resolved x-ray absorption spectroscopy on a femtosecond timescale, in combination with appropriate simulations, is able to provide crucial insights into the ultrafast processes that occur upon ionization due to its element-specific probing nature. In this theoretical study, we investigate the ultrafast dynamics of valence-ionized states of urea and its dimer employing Tully's fewest switches surface hopping approach using Koopmans' theorem to describe the ionized system. We demonstrate that following valence ionization through a pump pulse, the time-resolved x-ray absorption spectra at the carbon, nitrogen, and oxygen K-edges reveal rich insights into the dynamics. Excited states of the ionized system give rise to time-delayed blueshifts in the x-ray absorption spectra as a result of electronic relaxation dynamics through nonadiabatic transitions. Moreover, our statistical analysis reveals specific structural dynamics in the molecule that induce time-dependent changes in the spectra. For the urea monomer, we elucidate the possibility to trace effects of specific molecular vibrations in the time-resolved x-ray absorption spectra. For the urea dimer, where ionization triggers a proton transfer reaction, we show how the x-ray absorption spectra can reveal specific details on the progress of proton transfer.
研究电离后化学体系的早期动力学对我们了解辐射损伤至关重要。然而,由于这些过程的复杂性,实验和理论研究都非常具有挑战性。飞秒时间尺度的时间分辨 X 射线吸收光谱与适当的模拟相结合,能够提供电离后发生的超快过程的重要见解,因为它具有特定元素探测的性质。在这项理论研究中,我们采用 Tully 的最少开关表面跳跃方法,利用 Koopmans 定理来描述脲及其二聚物的价电离态的超快动力学。我们证明,在通过泵脉冲进行价电离之后,碳、氮和氧 K 边的时间分辨 X 射线吸收光谱揭示了丰富的动力学信息。电离体系的激发态通过非绝热跃迁的电子弛豫动力学,在 X 射线吸收光谱中产生了延时蓝移。此外,我们的统计分析还揭示了分子中的特定结构动力学,这些动力学会引起光谱的时变。对于脲单体,我们阐明了在时间分辨 X 射线吸收光谱中追踪特定分子振动效应的可能性。对于电离引发质子转移反应的脲二聚体,我们展示了 X 射线吸收光谱如何揭示质子转移过程的具体细节。
{"title":"Ultrafast time-resolved x-ray absorption spectroscopy of ionized urea and its dimer through <i>ab initio</i> nonadiabatic dynamics.","authors":"Yashoj Shakya, Ludger Inhester, Caroline Arnold, Ralph Welsch, Robin Santra","doi":"10.1063/4.0000076","DOIUrl":"10.1063/4.0000076","url":null,"abstract":"<p><p>Investigating the early dynamics of chemical systems following ionization is essential for our understanding of radiation damage. However, experimental as well as theoretical investigations are very challenging due to the complex nature of these processes. Time-resolved x-ray absorption spectroscopy on a femtosecond timescale, in combination with appropriate simulations, is able to provide crucial insights into the ultrafast processes that occur upon ionization due to its element-specific probing nature. In this theoretical study, we investigate the ultrafast dynamics of valence-ionized states of urea and its dimer employing Tully's fewest switches surface hopping approach using Koopmans' theorem to describe the ionized system. We demonstrate that following valence ionization through a pump pulse, the time-resolved x-ray absorption spectra at the carbon, nitrogen, and oxygen <i>K</i>-edges reveal rich insights into the dynamics. Excited states of the ionized system give rise to time-delayed blueshifts in the x-ray absorption spectra as a result of electronic relaxation dynamics through nonadiabatic transitions. Moreover, our statistical analysis reveals specific structural dynamics in the molecule that induce time-dependent changes in the spectra. For the urea monomer, we elucidate the possibility to trace effects of specific molecular vibrations in the time-resolved x-ray absorption spectra. For the urea dimer, where ionization triggers a proton transfer reaction, we show how the x-ray absorption spectra can reveal specific details on the progress of proton transfer.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-05-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8118673/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"39010118","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-05-03eCollection Date: 2021-05-01DOI: 10.1063/4.0000093
Deependra Jadoun, Mahesh Gudem, Markus Kowalewski
Many recent experimental ultrafast spectroscopy studies have hinted at non-adiabatic dynamics indicating the existence of conical intersections, but their direct observation remains a challenge. The rapid change of the energy gap between the electronic states complicated their observation by requiring bandwidths of several electron volts. In this manuscript, we propose to use the combined information of different x-ray pump-probe techniques to identify the conical intersection. We theoretically study the conical intersection in pyrrole using transient x-ray absorption, time-resolved x-ray spontaneous emission, and linear off-resonant Raman spectroscopy to gather evidence of the curve crossing.
最近的许多超快光谱实验研究都暗示了锥形交点存在的非绝热动态,但直接观测锥形交点仍然是一项挑战。电子态之间能隙的快速变化要求几个电子伏特的带宽,从而使其观测变得复杂。在本手稿中,我们提出利用不同 X 射线泵浦探针技术的综合信息来识别锥形交点。我们使用瞬态 X 射线吸收、时间分辨 X 射线自发辐射和线性非共振拉曼光谱对吡咯中的锥形交叉点进行了理论研究,以收集曲线交叉的证据。
{"title":"Capturing fingerprints of conical intersection: Complementary information of non-adiabatic dynamics from linear x-ray probes.","authors":"Deependra Jadoun, Mahesh Gudem, Markus Kowalewski","doi":"10.1063/4.0000093","DOIUrl":"10.1063/4.0000093","url":null,"abstract":"<p><p>Many recent experimental ultrafast spectroscopy studies have hinted at non-adiabatic dynamics indicating the existence of conical intersections, but their direct observation remains a challenge. The rapid change of the energy gap between the electronic states complicated their observation by requiring bandwidths of several electron volts. In this manuscript, we propose to use the combined information of different x-ray pump-probe techniques to identify the conical intersection. We theoretically study the conical intersection in pyrrole using transient x-ray absorption, time-resolved x-ray spontaneous emission, and linear off-resonant Raman spectroscopy to gather evidence of the curve crossing.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-05-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8096460/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38906633","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-15eCollection Date: 2021-03-01DOI: 10.1063/4.0000059
A Nakamura, T Shimojima, K Ishizaka
In this paper, we investigate the femtosecond-optical-pulse-induced strain dynamics in relatively thin (100 nm) and thick (10 000 nm) silicon plates based on finite-element simulations. In the thin sample, almost spatially homogeneous excitation by the optical pulse predominantly generates a standing wave of the lowest-order acoustic resonance mode along the out-of-plane direction. At the same time, laterally propagating plate waves are emitted at the sample edge through the open edge deformation. Fourier transformation analysis reveals that the plate waves in the thin sample are mainly composed of two symmetric Lamb waves, reflecting the spatially uniform photoexcitation. In the thick sample, on the other hand, only the near surface region is photo-excited and thus a strain pulse that propagates along the out-of-plane direction is generated, accompanying the laterally propagating pulse-like strain dynamics through the edge deformation. These lateral strain pulses consist of multiple Lamb waves, including asymmetric and higher-order symmetric modes. Our simulations quantitatively demonstrate the out-of-plane and in-plane photoinduced strain dynamics in realistic silicon plates, ranging from the plate wave form to pulse trains, depending on material parameters such as sample thickness, optical penetration depth, and sound velocity.
{"title":"Finite-element simulation of photoinduced strain dynamics in silicon thin plates.","authors":"A Nakamura, T Shimojima, K Ishizaka","doi":"10.1063/4.0000059","DOIUrl":"10.1063/4.0000059","url":null,"abstract":"<p><p>In this paper, we investigate the femtosecond-optical-pulse-induced strain dynamics in relatively thin (100 nm) and thick (10 000 nm) silicon plates based on finite-element simulations. In the thin sample, almost spatially homogeneous excitation by the optical pulse predominantly generates a standing wave of the lowest-order acoustic resonance mode along the out-of-plane direction. At the same time, laterally propagating plate waves are emitted at the sample edge through the open edge deformation. Fourier transformation analysis reveals that the plate waves in the thin sample are mainly composed of two symmetric Lamb waves, reflecting the spatially uniform photoexcitation. In the thick sample, on the other hand, only the near surface region is photo-excited and thus a strain pulse that propagates along the out-of-plane direction is generated, accompanying the laterally propagating pulse-like strain dynamics through the edge deformation. These lateral strain pulses consist of multiple Lamb waves, including asymmetric and higher-order symmetric modes. Our simulations quantitatively demonstrate the out-of-plane and in-plane photoinduced strain dynamics in realistic silicon plates, ranging from the plate wave form to pulse trains, depending on material parameters such as sample thickness, optical penetration depth, and sound velocity.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-04-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1063/4.0000059","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38914126","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2021-04-08eCollection Date: 2021-03-01DOI: 10.1063/4.0000086
Yanqin Zhai, Nicos S Martys, William L George, Joseph E Curtis, Jannatun Nayem, Y Z, Yun Liu
In the past decade, there was increased research interest in studying internal motions of flexible proteins in solution using Neutron Spin Echo (NSE) as NSE can simultaneously probe the dynamics at the length and time scales comparable to protein domain motions. However, the collective intermediate scattering function (ISF) measured by NSE has the contributions from translational, rotational, and internal motions, which are rather complicated to be separated. Widely used NSE theories to interpret experimental data usually assume that the translational and rotational motions of a rigid particle are decoupled and independent to each other. To evaluate the accuracy of this approximation for monoclonal antibody (mAb) proteins in solution, dissipative particle dynamic computer simulation is used here to simulate a rigid-body mAb for up to about 200 ns. The total ISF together with the ISFs due to only the translational and rotational motions as well as their corresponding effective diffusion coefficients is calculated. The aforementioned approximation introduces appreciable errors to the calculated effective diffusion coefficients and the ISFs. For the effective diffusion coefficient, the error introduced by this approximation can be as large as about 10% even though the overall agreement is considered reasonable. Thus, we need to be cautious when interpreting the data with a small signal change. In addition, the accuracy of the calculated ISFs due to the finite computer simulation time is also discussed.
{"title":"Intermediate scattering functions of a rigid body monoclonal antibody protein in solution studied by dissipative particle dynamic simulation.","authors":"Yanqin Zhai, Nicos S Martys, William L George, Joseph E Curtis, Jannatun Nayem, Y Z, Yun Liu","doi":"10.1063/4.0000086","DOIUrl":"10.1063/4.0000086","url":null,"abstract":"<p><p>In the past decade, there was increased research interest in studying internal motions of flexible proteins in solution using Neutron Spin Echo (NSE) as NSE can simultaneously probe the dynamics at the length and time scales comparable to protein domain motions. However, the collective intermediate scattering function (ISF) measured by NSE has the contributions from translational, rotational, and internal motions, which are rather complicated to be separated. Widely used NSE theories to interpret experimental data usually assume that the translational and rotational motions of a rigid particle are decoupled and independent to each other. To evaluate the accuracy of this approximation for monoclonal antibody (mAb) proteins in solution, dissipative particle dynamic computer simulation is used here to simulate a rigid-body mAb for up to about 200 ns. The total ISF together with the ISFs due to only the translational and rotational motions as well as their corresponding effective diffusion coefficients is calculated. The aforementioned approximation introduces appreciable errors to the calculated effective diffusion coefficients and the ISFs. For the effective diffusion coefficient, the error introduced by this approximation can be as large as about 10% even though the overall agreement is considered reasonable. Thus, we need to be cautious when interpreting the data with a small signal change. In addition, the accuracy of the calculated ISFs due to the finite computer simulation time is also discussed.</p>","PeriodicalId":48683,"journal":{"name":"Structural Dynamics-Us","volume":null,"pages":null},"PeriodicalIF":2.8,"publicationDate":"2021-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8034984/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"38885685","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}