TY - JOUR A1 - Wolf, Thomas J. A. A1 - Sanchez, David M. A1 - Yang, J. A1 - Parrish, R. M. A1 - Nunes, J. P. F. A1 - Centurion, M. A1 - Coffee, R. A1 - Cryan, J. P. A1 - Gühr, Markus A1 - Hegazy, Kareem A1 - Kirrander, Adam A1 - Li, R. K. A1 - Ruddock, J. A1 - Shen, Xiaozhe A1 - Vecchione, T. A1 - Weathersby, S. P. A1 - Weber, Peter M. A1 - Wilkin, K. A1 - Yong, Haiwang A1 - Zheng, Q. A1 - Wang, X. J. A1 - Minitti, Michael P. A1 - Martinez, Todd J. T1 - The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction JF - Nature chemistry N2 - The ultrafast photoinduced ring-opening of 1,3-cyclohexadiene constitutes a textbook example of electrocyclic reactions in organic chemistry and a model for photobiological reactions in vitamin D synthesis. Although the relaxation from the photoexcited electronic state during the ring-opening has been investigated in numerous studies, the accompanying changes in atomic distance have not been resolved. Here we present a direct and unambiguous observation of the ring-opening reaction path on the femtosecond timescale and subangstrom length scale using megaelectronvolt ultrafast electron diffraction. We followed the carbon-carbon bond dissociation and the structural opening of the 1,3-cyclohexadiene ring by the direct measurement of time-dependent changes in the distribution of interatomic distances. We observed a substantial acceleration of the ring-opening motion after internal conversion to the ground state due to a steepening of the electronic potential gradient towards the product minima. The ring-opening motion transforms into rotation of the terminal ethylene groups in the photoproduct 1,3,5-hexatriene on the subpicosecond timescale. KW - Organic chemistry KW - Photochemistry KW - Physical chemistry KW - Theoretical chemistry Y1 - 2019 U6 - https://doi.org/10.1038/s41557-019-0252-7 SN - 1755-4330 SN - 1755-4349 VL - 11 IS - 6 SP - 504 EP - 509 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Tong, Yujin A1 - Wirth, Jonas A1 - Kirsch, Harald A1 - Wolf, Martin A1 - Saalfrank, Peter A1 - Campen, Richard Kramer T1 - Optically probing Al-O and O-H vibrations to characterize water adsorption and surface reconstruction on alpha-alumina: An experimental and theoretical study JF - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr N2 - Oxide/water interfaces are ubiquitous in a wide variety of applications and the environment. Despite this ubiquity, and attendant decades of study, gaining molecular level insight into water/oxide interaction has proven challenging. In part, this challenge springs from a lack of tools to concurrently characterize changes in surface structure (i.e., water/oxide interaction from the perspective of the solid) and O-H population and local environment (i.e., water/oxide interaction from the water perspective). Here, we demonstrate the application of surface specific vibrational spectroscopy to the characterization of the interaction of the paradigmatic alpha-Al2O3(0001) surface and water. By probing both the interfacial Al-O (surface phonon) and O-H spectral response, we characterize this interaction from both perspectives. Through electronic structure calculation, we assign the interfacial Al-O response and rationalize its changes on surface dehydroxylation and reconstruction. Because our technique is all-optical and interface specific, it is equally applicable to oxide surfaces in vacuum, ambient atmospheres and at the solid/liquid interface. Application of this approach to additional alumina surfaces and other oxides thus seems likely to significantly expand our understanding of how water meets oxide surfaces and thus the wide variety of phenomena this interaction controls. (C) 2015 AIP Publishing LLC. Y1 - 2015 U6 - https://doi.org/10.1063/1.4906346 SN - 0021-9606 SN - 1089-7690 VL - 142 IS - 5 PB - American Institute of Physics CY - Melville ER - TY - JOUR A1 - Kirsch, Harald A1 - Wirth, Jonas A1 - Tong, Yujin A1 - Wolf, Martin A1 - Saalfrank, Peter A1 - Campen, Richard Kramer T1 - Experimental characterization of unimolecular water dissociative adsorption on alpha-alumina JF - The journal of physical chemistry : C, Nanomaterials and interfaces N2 - alpha-Al2O3 surfaces are common in both engineered applications and the environment. Much prior work indicates that their properties, e.g., reactivity, polarity, and charge, change dramatically on interaction with water. Perhaps the simplest question that can be asked of alpha-Al2O3/water interaction is how a single water molecule interacts with the most stable alpha-Al2O3 surface: the alpha-Al2O3(0001). Over the last 15 years, a series of theoretical studies have found that water dissociatively adsorbs on alpha-Al2O3(0001) through two channels. However, to our knowledge no experimental evidence of these dissociation pathways has appeared. By combining sample preparation via supersonic molecular beam dosing, sample characterization via coherent, surface specific vibrational spectroscopy and electronic structure theory, we report the first experimental observation of reaction products of each, theoretically predicted, dissociation channel. These results thus overcome a 15 year old experiment/theory disconnect and make possible a variety of intriguing experiments that promise to provide significant new insights into water/Al2O3 and water/oxide interaction more generally. Y1 - 2014 U6 - https://doi.org/10.1021/jp502106t SN - 1932-7447 VL - 118 IS - 25 SP - 13623 EP - 13630 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Mayer, Dennis A1 - Lever, Fabiano A1 - Picconi, David A1 - Metje, Jan A1 - Ališauskas, Skirmantas A1 - Calegari, Francesca A1 - Düsterer, Stefan A1 - Ehlert, Christopher A1 - Feifel, Raimund A1 - Niebuhr, Mario A1 - Manschwetus, Bastian A1 - Kuhlmann, Marion A1 - Mazza, Tommaso A1 - Robinson, Matthew Scott A1 - Squibb, Richard J. A1 - Trabattoni, Andrea A1 - Wallner, Måns A1 - Saalfrank, Peter A1 - Wolf, Thomas J. A. A1 - Gühr, Markus T1 - Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy JF - Nature communications N2 - Imaging the charge flow in photoexcited molecules would provide key information on photophysical and photochemical processes. Here the authors demonstrate tracking in real time after photoexcitation the change in charge density at a specific site of 2-thiouracil using time-resolved X-ray photoelectron spectroscopy. The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states. Y1 - 2022 U6 - https://doi.org/10.1038/s41467-021-27908-y SN - 2041-1723 N1 - Publisher correction: https://doi.org/10.1038/s41467-022-28584-2 VL - 13 IS - 1 PB - Nature Research CY - Berlin ER -