55493
2017
2016
eng
116
126
11
38
article
Wiley-Blackwell
Hoboken
1
2016-11-09
2016-11-09
--
The quest for best suited references for configuration interaction singles calculations of core excited states
Near edge X-ray absorption fine structure (NEXAFS) simulations based on the conventional configuration interaction singles (CIS) lead to excitation energies, which are systematically blue shifted. Using a (restricted) open shell core hole reference instead of the Hartree Fock (HF) ground state orbitals improves (Decleva et al., Chem. Phys., 1992, 168, 51) excitation energies and the shape of the spectra significantly. In this work, we systematically vary the underlying SCF approaches, that is, based on HF or density functional theory, to identify best suited reference orbitals using a series of small test molecules. We compare the energies of the K edges and NEXAFS spectra to experimental data. The main improvement compared to conventional CIS, that is, using HF ground state orbitals, is due to the electrostatic influence of the core hole. Different SCF approaches, density functionals, or the use of fractional occupations lead only to comparably small changes. Furthermore, to account for bigger systems, we adapt the core-valence separation for our approach. We demonstrate that the good quality of the spectrum is not influenced by this approximation when used together with the non-separated ground state wave function. Simultaneously, the computational demands are reduced remarkably. (C) 2016 Wiley Periodicals, Inc.
Journal of computational chemistry : organic, inorganic, physical, biological
10.1002/jcc.24531
27862049
0192-8651
1096-987X
wos:2017
WOS:000388916500007
Klamroth, T (reprint author), Univ Potsdam, Inst Chem, Theoret Chem, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany., klamroth@uni-potsdam.de
2022-07-07T09:52:30+00:00
sword
importub
filename=package.tar
e6cf21795bc9992e265962b6c813258c
Klamroth, Tillmann
false
true
Christopher Ehlert
Tillmann Klamroth
eng
uncontrolled
core excited states
eng
uncontrolled
configuration interaction
eng
uncontrolled
near edge X-ray absorption fine structure
Chemie und zugeordnete Wissenschaften
Institut für Chemie
Referiert
Import
38518
2015
2015
eng
10117
10124
8
19
87
article
American Chemical Society
Washington
1
--
--
--
Quantification of Silane Molecules on Oxidized Silicon: Are there Options for a Traceable and Absolute Determination?
Organosilanes are used routinely to functionalize various support materials for further modifications. Nevertheless, reliable quantitative information about surface functional group densities after layer formation is rarely available. Here, we present the analysis of thin organic nanolayers made from nitrogen containing silane molecules on naturally oxidized silicon wafers with reference-free total reflection X-ray fluorescence (TXR.F) and X-ray photoelectron spectroscopy (XPS). An areic density of 2-4 silane molecules per nm(2) was calculated from the layer's nitrogen mass deposition per area unit obtained by reference-free TXRF. Complementary energy and angle-resolved XPS (ER/AR-XPS) in the Si 2p core-level region was used to analyze the outermost surface region of the organic (silane layer)-inorganic (silicon wafer) interface. Different coexisting silicon species as silicon, native silicon oxide, and silane were identified and quantified. As a result of the presented proof-of-concept, absolute and traceable values for the areic density of silanes containing nitrogen as intrinsic marker are obtained by calibration of the XPS methods with reference-free TXRF. Furthermore, ER/AR-XPS is shown to facilitate the determination of areic densities in (mono)layers made from silanes having no heteroatomic marker other than silicon. After calibration with reference-free TXRF, these areic densities of silane molecules can be determined when using the XPS component intensity of the silane's silicon atom.
Analytical chemistry
10.1021/acs.analchem.5b02846
26334589
0003-2700
1520-6882
wos:2015
WOS:000362628600085
Dietrich, PM (reprint author), Bundesanstalt Matforsch & Prufung BAM, Unter Eichen 87, D-12205 Berlin, Germany., paul.dietrich@bam.de
European Union through the European Metrology Research Program (EMRP);
EMRP within EURAMET; European Union
Paul M. Dietrich
Cornelia Streeck
Stephan Glamsch
Christopher Ehlert
Andreas Lippitz
Andreas Nutsch
Nora Kulak
Burkhard Beckhoff
W. E. S. Unger
Institut für Chemie
Referiert
45610
2016
2016
eng
406
411
6
363
article
Elsevier
Amsterdam
1
--
--
--
Synchrotron-radiation XPS analysis of ultra-thin silane films: Specifying the organic silicon
The analysis of chemical and elemental in-depth variations in ultra-thin organic layers with thicknesses below 5 nm is very challenging. Energy- and angle-resolved XPS (ER/AR-XPS) opens up the possibility for non-destructive chemical ultra-shallow depth profiling of the outermost surface layer of ultra-thin organic films due to its exceptional surface sensitivity. For common organic materials a reliable chemical in-depth analysis with a lower limit of the XPS information depth z(95) of about 1 nm can be performed. As a proof-of-principle example with relevance for industrial applications the ER/AR-XPS analysis of different organic monolayers made of amino- or benzamidosilane molecules on silicon oxide surfaces is presented. It is demonstrated how to use the Si 2p core-level region to non-destructively depth-profile the organic (silane monolayer) - inorganic (SiO2/Si) interface and how to quantify Si species, ranging from elemental silicon over native silicon oxide to the silane itself. The main advantage of the applied ER/AR-XPS method is the improved specification of organic from inorganic silicon components in Si 2p core-level spectra with exceptional low uncertainties compared to conventional laboratory XPS. (C) 2015 Elsevier B.V. All rights reserved.
Applied surface science : a journal devoted to applied physics and chemistry of surfaces and interfaces
10.1016/j.apsusc.2015.12.052
0169-4332
1873-5584
wos2016:2019
WOS:000370572400052
Dietrich, PM (reprint author), Bundesanstalt Mat Forsch & Prufung BAM, Unter Eichen 87, D-12205 Berlin, Germany., paul.dietrich@yahoo.de
European Union through the European Metrology Research Program (EMRP); EMRP participating countries within EURAMET; European Union
importub
2020-03-22T19:58:01+00:00
filename=package.tar
87d93672388badba15a6d30dbd0384a3
Paul M. Dietrich
Stephan Glamsch
Christopher Ehlert
Andreas Lippitz
Nora Kulak
Wolfgang E. S. Unger
eng
uncontrolled
Synchrotron radiation XPS
eng
uncontrolled
Depth profiling
eng
uncontrolled
Silanes
eng
uncontrolled
Monolayer
eng
uncontrolled
Amines
eng
uncontrolled
Amides
Institut für Chemie
Referiert
Import
44740
2016
2016
eng
11235
11249
15
81
article
American Chemical Society
Washington
1
--
--
--
Systematic Investigation into the Matsuda-Heck Reaction of alpha-Methylene Lactones: How Conformational Constraints Direct the beta-H-Elimination Step
alpha-Methylene-gamma-butyrolactone and alpha-methylene-gamma-valerolactone undergo Pd-catalyzed Matsuda-Heck couplings with arene diazonium salts to alpha-benzyl butenolides or pentenolides, respectively, or to alpha-benzylidene lactones. The observed regioselectivity is strongly ring size dependent, with six-membered rings giving exclusively alpha-benzyl pentenolides, whereas the five-membered alpha-methylene lactone reacts to mixtures of regioisomers with a high proportion of (E)-alpha-benzylidene-gamma-butyrolactones. DFT calculations suggest that the reasons for these differences are not thermodynamic but kinetic in nature. The relative energies of the conformers of the Pd sigma-complexes resulting from insertion into the Pd-aryl bond were correlated with the dihedral angles between Pd and endo-beta-H. This correlation revealed that in the case of the six-membered lactone an energetically favorable conformer adopts a nearly synperiplanar Pd/endo-beta-H arrangement, whereas for the analogous Pd sigma-complex of the five-membered lactone the smallest Pd/endo-beta-H dihedral angle is observed for a conformer with a comparatively high potential energy. The optimized conditions for Matsuda-Heck arylations of exo-methylene lactones were eventually applied to the synthesis of the natural product anemarcoumarin A.
The journal of organic chemistry
10.1021/acs.joc.6b02207
27750013
0022-3263
wos2016:2019
WOS:000391248800061
Schmidt, B (reprint author), Univ Potsdam, Inst Chem, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany., bernd.schmidt@uni-potsdam.de
importub
2020-03-22T12:42:01+00:00
filename=package.tar
534b745937549b33e7832128ac87eb73
Bernd Schmidt
Felix Wolf
Christopher Ehlert
Institut für Chemie
Referiert
Import
60643
2020
2020
eng
1781
1789
9
19
41
article
Wiley
Hoboken
1
2020-05-12
2020-05-12
--
PSIXAS: A Psi4 plugin for efficient simulations of X-ray absorption spectra based on the transition-potential and Delta-Kohn-Sham method
Near edge X-ray absorption fine structure (NEXAFS) spectra and their pump-probe extension (PP-NEXAFS) offer insights into valence- and core-excited states. We present PSIXAS, a recent implementation for simulating NEXAFS and PP-NEXAFS spectra by means of the transition-potential and the Delta-Kohn-Sham method. The approach is implemented in form of a software plugin for the Psi4 code, which provides access to a wide selection of basis sets as well as density functionals. We briefly outline the theoretical foundation and the key aspects of the plugin. Then, we use the plugin to simulate PP-NEXAFS spectra of thymine, a system already investigated by others and us. It is found that larger, extended basis sets are needed to obtain more accurate absolute resonance positions. We further demonstrate that, in contrast to ordinary NEXAFS simulations, where the choice of the density functional plays a minor role for the shape of the spectrum, for PP-NEXAFS simulations the choice of the density functional is important. Especially hybrid functionals (which could not be used straightforwardly before to simulate PP-NEXAFS spectra) and their amount of "Hartree-Fock like" exact exchange affects relative resonance positions in the spectrum.
Journal of computational chemistry : organic, inorganic, physical, biological
10.1002/jcc.26219
32394459
0192-8651
1096-987X
outputup:dataSource:WoS:2020
WOS:000531556200001
Ehlert, C (corresponding author), Heidelberg Inst Theoret Studies HITS gGmbH, Schloss Wolfsbrunnenweg 35, D-69118 Heidelberg, Germany., christopher.ehlert@h-its.org
Ehlert, Christopher
2023-09-04T09:12:42+00:00
sword
importub
filename=package.tar
8025dcbee6ed28532b2dad5604a908a2
1479181-X
282917-4
false
true
CC-BY - Namensnennung 4.0 International
Christopher Ehlert
Tillmann Klamroth
eng
uncontrolled
transition-potential method
eng
uncontrolled
X-ray absorption
eng
uncontrolled
spectroscopy
eng
uncontrolled
Delta-Kohn-Sham
Chemie und zugeordnete Wissenschaften
Institut für Chemie
Referiert
Import
51488
2018
2018
eng
13
14
149
article
American Institute of Physics
Melville
1
2018-10-11
2018-10-11
--
An efficient first principles method for molecular pump-probe NEXAFS spectra
Pump-probe near edge X-ray absorption fine structure (PP-NEXAFS) spectra of molecules offer insight into valence-excited states, even if optically dark. In PP-NEXAFS spectroscopy, the molecule is "pumped" by UV or visible light enforcing a valence excitation, followed by an X-ray "probe" exciting core electrons into (now) partially empty valence orbitals. Calculations of PP-NEXAFS have so far been done by costly, correlated wavefunction methods which are not easily applicable to medium-sized or large molecules. Here we propose an efficient, first principles method based on density functional theory in combination with the transition potential and Delta SCF methodology (TP-DFT/Delta SCF) to compute molecular ground state and PP-NEXAFS spectra. We apply the method to n ->pi* pump/O-K-edge NEXAFS probe spectroscopy of thymine (for which both experimental and other theoretical data exist) and to n -> pi* or pi -> pi* pump/N-K-edge NEXAFS probe spectroscopies of trans-and cis-azobenzene. Published by AIP Publishing.
The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
application to thymine and azobenzene
10.1063/1.5050488
30316280
0021-9606
1089-7690
wos:2018
144112
WOS:000447149500016
Ehlert, C (reprint author), Wilfrid Laurier Univ, Dept Chem & Biochem, 75 Univ Ave W, Waterloo, ON N2L 3C5, Canada.
DFG (German Research Council) through the Cluster of Excellence "Unifying Concepts in Catalysis" [304]; SOSCIP Consortium (TalentEdge program); Lichtenberg professorship of the Volkswagen foundation
2021-08-06T06:49:09+00:00
sword
importub
filename=package.tar
6d26e929af3abc2d204894259a974eac
Ehlert, Christopher
false
true
Christopher Ehlert
Markus Gühr
Peter Saalfrank
Chemie und zugeordnete Wissenschaften
Institut für Physik und Astronomie
Institut für Chemie
Referiert
Import
57744
2022
2022
eng
9
1301
postprint
1
2022-01-11
2022-01-11
--
Following excited-state chemical shifts in molecular ultrafast 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.
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
10.25932/publishup-57744
urn:nbn:de:kobv:517-opus4-577442
1866-8372
These authors contributed equally: D. Mayer, F. Lever.
A Publisher Correction to this article was published on 09 March 2022.
This article has been updated.
Version of record
<a href="http://publishup.uni-potsdam.de/57743">Bibliographieeintrag der Originalveröffentlichung/Quelle</a>
Gühr, Marcus
Picconi, David
CC-BY - Namensnennung 4.0 International
Dennis Mayer
Fabiano Lever
David Picconi
Jan Metje
Skirmantas Ališauskas
Francesca Calegari
Stefan Düsterer
Christopher Ehlert
Raimund Feifel
Mario Niebuhr
Bastian Manschwetus
Marion Kuhlmann
Tommaso Mazza
Matthew Scott Robinson
Richard James Squibb
Andrea Trabattoni
Måns Wallner
Peter Saalfrank
Thomas J. A. Wolf
Markus Gühr
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
1301
Physik
open_access
Institut für Physik und Astronomie
Referiert
Green Open-Access
Universität Potsdam
https://publishup.uni-potsdam.de/files/57744/pmnr1301.pdf
45500
2016
2016
eng
8654
8661
8
18
article
Royal Society of Chemistry
Cambridge
1
--
--
--
A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids
In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([C(n)C(1)im](+)[NTf2](-) and [C(4)C(1)im](+)[I](-)). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
Physical chemistry, chemical physics : a journal of European Chemical Societies
10.1039/c5cp07434g
26948544
1463-9076
1463-9084
wos2016:2019
WOS:000372249100036
Saalfrank, P (reprint author), Univ Potsdam, Inst Chem, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany., peter.saalfrank@uni-potsdam.de
BAM as part of the BAM MIS Program [Ideen_2012_59]; Austrian Science Found (FWF) through the Erwin-Schrodinger fellowship program [J 3471-N28]
importub
2020-03-22T19:03:01+00:00
filename=package.tar
6fc5074a9ae2206e9db08f4cc1e21426
Christopher Ehlert
Markus Holzweber
Andreas Lippitz
Wolfgang E. S. Unger
Peter Saalfrank
Institut für Chemie
Referiert
Import
36704
2011
2011
eng
1516
1524
9
15-16
605
article
Elsevier
Amsterdam
1
--
--
--
Ab initio calculations for XPS chemical shifts of poly(vinyl-trifluoroacetate) using trimer models
X-ray photoelectron spectra (XPS) of the polymer poly(vinyl-trifluoroacetate) show C(1s) binding energy shifts which are unusual because they are influenced by atoms which are several bonds away from the probed atom. In this work, the influence of the trifluoroacetate substituent on the 1s ionization potential of the carbon atoms of the polyethylene chain is investigated theoretically using mono-substituted, diad and triad models of trimers representing the polymer. Carbon 1s ionization energies are calculated by the Hartree-Fock theory employing Koopmans' theorem. The influence of the configuration and conformation of the functional groups as well as the degree of substitution are found to be important determinants of XPS spectra. It is further found that the 1s binding energy correlates in a linear fashion, with the total electrostatic potential at the position of the probe atom, and depends not only on nearest neighbor effects. This may have implications for the interpretation of high-resolution XP spectra.
Surface science
10.1016/j.susc.2011.05.021
0039-6028
wos:2011-2013
WOS:000293671000030
Kroner, D (reprint author), Univ Potsdam, Dept Chem, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany., Dominik.Kroener@uni-potsdam.de; Peter.Saalfrank@uni-potsdam.de; andreas.hollaender@iap.fraunhofer.de
Dominik Kröner
Christopher Ehlert
Peter Saalfrank
Andreas Holländer
eng
uncontrolled
Ab initio quantum chemical methods and calculations
eng
uncontrolled
X-ray photoelectron spectroscopy
eng
uncontrolled
Insulating films
Institut für Chemie
Referiert
39192
2015
2015
eng
38
45
8
199
article
Elsevier
Amsterdam
1
--
--
--
A combined quantum chemical/molecular dynamics study of X-ray photoelectron spectra of polyvinyl alcohol using oligomer models
X-ray photoelectron spectroscopy (XPS) is a powerful tool for probing the local chemical environment of atoms near surfaces. When applied to soft matter, such as polymers, XPS spectra are frequently shifted and broadened due to thermal atom motion and by interchain interactions. We present a combined quantum mechanical QM/molecular dynamics (MD) simulation of X-ray photoelectron spectra of polyvinyl alcohol (PVA) using oligomer models in order to account for and quantify these effects on the XPS (C1s) signal. In our study, molecular dynamics at finite temperature were performed with a classical forcefield and by ab initio MD (AIMD) using the Car-Parrinello method. Snapshots along, the trajectories represent possible conformers and/or neighbouring environments, with different C1s ionization potentials for individual C atoms leading to broadened XPS peaks. The latter are determined by Delta-Kohn Sham calculations. We also examine the experimental practice of gauging XPS (C1s) signals of alkylic C-atoms in C-containing polymers to the C1s signal of polyethylene.
We find that (i) the experimental XPS (C1s) spectra of PVA (position and width) can be roughly represented by single-strand models, (ii) interchain interactions lead to red-shifts of the XPS peaks by about 0.6 eV, and (iii) AIMD simulations match the findings from classical MD semi-quantitatively. Further, (iv) the gauging procedure of XPS (C1s) signals to the values of PE, introduces errors of about 0.5 eV. (C) 2014 Elsevier B.V. All rights reserved.
Journal of electron spectroscopy and related phenomena : the international journal on theoretical and experimental aspects of electron spectroscopy
10.1016/j.elspec.2014.12.007
0368-2048
1873-2526
wos:2015
WOS:000350834300005
Saalfrank, P (reprint author), Univ Potsdam, Inst Chem, Karl Liebknecht Str 24-25, D-14476 Golm, Germany., Peter.Saalfrank@uni-potsdam.de
BAM (BAM MIS programme) [Ideen_2012_59]
Christopher Ehlert
Dominik Kröner
Peter Saalfrank
eng
uncontrolled
Simulation of polymer XPS
eng
uncontrolled
Delta-Kohn Sham method
eng
uncontrolled
Thermal broadening effects
eng
uncontrolled
Interchain interactions
eng
uncontrolled
Classical MD
eng
uncontrolled
Poly vinyl alcohol
Institut für Chemie
Referiert
38271
2014
2014
eng
14083
14095
13
27
16
article
Royal Society of Chemistry
Cambridge
1
--
--
--
C K-edge NEXAFS spectra of graphene with physical and chemical defects: a study based on density functional theory
Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.
Physical chemistry, chemical physics : a journal of European Chemical Societies
10.1039/c4cp01106f
24901898
1463-9076
1463-9084
wos:2014
WOS:000338116700058
Unger, WES (reprint author), BAM Bundesanstalt Mat Forsch & Prufung, D-12203 Berlin, Germany., wolfgang.unger@bam.de; petsaal@uni-potsdam.de
BAM Presidium [Ideen_2012_59]
Christopher Ehlert
Wolfgang E. S. Unger
Peter Saalfrank
Institut für Chemie
Referiert
53111
2018
2018
eng
3172
3177
6
4
12
article
American Chemical Society
Washington
1
2018-02-28
2018-04-24
--
Control of oxidation and spin state in a single-molecule junction
The oxidation and spin state of a metal-organic molecule determine its chemical reactivity and magnetic properties. Here, we demonstrate the reversible control of the oxidation and spin state in a single Fe porphyrin molecule in the force field of the tip of a scanning electron tunneling microscope. Within the regimes of half-integer and integer spin state, we can further track the evolution of the magnetocrystalline anisotropy. Our experimental results are corroborated by density functional theory and wave function theory. This combined analysis allows us to draw a complete picture of the molecular states over a large range of intramolecular deformations.
ACS nano
10.1021/acsnano.8b00312
29489330
1936-0851
1936-086X
wos:2018
WOS:000431088200012
Franke, KJ (reprint author), Free Univ Berlin, Fachbereich Phys, Arnimallee 14, D-14195 Berlin, Germany.; Saalfrank, P (reprint author), Univ Potsdam, Inst Chem, Karl Liebknecht Str 24-25, D-14476 Potsdam, Germany., peter.saalfrank@uni-potsdam.de; franke@physik.fu-berlin.de
Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [Sfb 658, HE7368/2]; European Research Council through the consolidator grant "NanoSpin"; SOSCIP Consortium (TalentEdge program)
2021-12-13T15:25:47+00:00
sword
importub
filename=package.tar
df40177c76676a16a784c6db79d5ba03
false
true
Benjamin W. Heinrich
Christopher Ehlert
Nino Hatter
Lukas Braun
Christian Lotze
Peter Saalfrank
Katharina J. Franke
eng
uncontrolled
porphyrin
eng
uncontrolled
oxidation state
eng
uncontrolled
spin state
eng
uncontrolled
scanning tunneling microscopy
eng
uncontrolled
scanning tunneling spectroscopy
eng
uncontrolled
density functional theory
Physik
Institut für Physik und Astronomie
Referiert
Import
Green Open-Access
57743
2022
2022
eng
9
13
article
Springer Nature
Berlin
1
2022-01-11
2022-01-11
--
Following excited-state chemical shifts in molecular ultrafast 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.
Nature Communications
10.1038/s41467-021-27908-y
2041-1723
These authors contributed equally: D. Mayer, F. Lever.
A Publisher Correction to this article was published on 09 March 2022.
This article has been updated.
198
Gühr, Markus
2553671-0
<a href="https://doi.org/10.25932/publishup-57744">Zweitveröffentlichung in der Schriftenreihe Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 1301</a>
Universität Potsdam
PA 2022_146
5390,70
Picconi, David
Deutsche Forschungsgemeinschaft (DFG)
Projektnummer 491466077
CC-BY - Namensnennung 4.0 International
Dennis Mayer
Fabiano Lever
David Picconi
Jan Metje
Skirmantas Ališauskas
Francesca Calegari
Stefan Düsterer
Christopher Ehlert
Raimund Feifel
Mario Niebuhr
Bastian Manschwetus
Marion Kuhlmann
Tommaso Mazza
Matthew Scott Robinson
Richard James Squibb
Andrea Trabattoni
Måns Wallner
Peter Saalfrank
Thomas J. A. Wolf
Markus Gühr
Physik
Institut für Physik und Astronomie
Referiert
Publikationsfonds der Universität Potsdam
Gold Open-Access
10484
2016
2016
2017
deu
142
doctoralthesis
1
--
--
2017-02-27
Simulationen von Röntgenabsorptionsprozessen zur Charakterisierung von Systemen in kondensierter Phase
Simulation of X-ray absorption processes to characterize condensed phase systems
Die vorgelegte Dissertation präsentiert wissenschaftliche Ergebnisse, die in der Zeit vom Dezember 2012 bis August 2016, erarbeitet wurden. Der zentrale Inhalt der Arbeit ist die Simulation von Röntgenabsorptionsprozessen von verschiedenen Systemen in kondensierter Phase. Genauer gesagt, werden Nahkantenabsorptions- (NEXAFS) sowie Röntgenphotoelektronenspektren (XPS) berechnet. In beiden Fällen wird ein Röntgenphoton von einem molekularen System absorbiert. Aufgrund der hohen Photonenenergie wird ein stark gebundenes kernnahes Elektron angeregt. Bei der XPS gelangt dieses mit einer zu messenden kinetischen Energie in Kontinuumszustände. In Abhängigkeit der eingestrahlten Photonenenergie und der kinetischen Energie des austreten Elektrons, kann die Bindungsenergie berechnet werden, welche die zentrale Größe der XPS ist. Im Falle der NEXAFS-Spektroskopie wird das kernnahe Elektron in unbesetzte gebundene Zustände angeregt. Die zentrale Größe ist die Absorption als Funktion der eingestrahlten Photonenenergie. Das erste Kapitel meiner Arbeit erörtert detailliert die experimentellen Methoden sowie die daraus gewonnenen charakteristischen Größen.
Die experimentellen Spektren zeigen oft viele Resonanzen, deren Interpretation aufgrund fehlender Referenzmaterialien schwierig ist. In solchen Fällen bietet es sich an, die Spektren mittels quantenchemischer Methoden zu simulieren. Der dafür erforderliche mathematisch-physikalische Methodenkatalog wird im zweiten Kapitel der Arbeit erörtert.
Das erste von mir untersuchte System ist Graphen. In experimentellen Arbeiten wurde die Oberfläche mittels Bromplasma modifiziert. Die im Anschluss gemessenen NEXAFS-Spektren unterscheiden sich maßgeblich von den Spektren der unbehandelten Oberfläche. Mithilfe periodischer DFT-Rechnungen wurden verschiedene Gitterdefekte sowie bromierte Systeme untersucht und die NEXAFS-Spektren simuliert. Mittels der Simulationen können die Beiträge verschiedener Anregungszentren analysiert werden. Die Berechnungen erlauben den Schluss, dass Gitterdefekte maßgeblich für die entstandenen Veränderungen verantwortlich sind.
Polyvinylalkohol (PVA) wurde als zweites System behandelt. Hierbei sollte untersucht werden, wie groß der Einfluss der Molekularbewegung auf die Verbreiterung der Peaks im XP-Spektrum ist. Des Weiteren wurde untersucht, wie groß der Einfluss von intermolekularen Wechselwirkungen auf die Peakpositionen und Peakverbreiterung ist. Für die Berechnung dieses Systems wurde eine Kombination aus molekulardynamischen und quantenchemischen Methoden verwendet. Als Strukturen dienten Oligomermodelle, die unter dem Einfluss eines (ab initio) Potentials propagiert wurden. Entlang der erstellten Trajektorie wurden Schnappschüsse der Geometrien extrahiert und für die Berechnung der XP-Spektren verwendet. Die Spektren werden bereits mithilfe klassischer Molekulardynamik sehr gut reproduziert. Die erhaltenen Peakbreiten sind verglichen mit dem Experiment allerdings zu klein. Die Hauptursache der Peakverbreiterung ist die Molekularbewegung. Intermolekulare Wechselwirkungen verschieben die Peakpositionen um 0.6 eV zu kleineren Anregungsenergien.
Im dritten Teil der Arbeit stehen die NEXAFS-Spektren von ionischen Flüssigkeiten (ILs) im Fokus. Die experimentell gefundenen Spektren zeigen eine komplexe Struktur mit vielen Resonanzen. In der Arbeit wurden zwei ILs untersucht. Als Geometrien verwenden wir Clustermodelle, die aus experimentellen Kristallstrukturen extrahiert wurden. Die berechneten Spektren erlauben es, die Resonanzen den Anregungszentren zuzuordnen. Außerdem kann eine erstmals gemessene Doppelresonanz simuliert und erklärt werden. Insgesamt kann die Interpretation der Spektren mithilfe der Simulation signifikant erweitert werden.
In allen Systemen wurde zur Berechnung des NEXAFS-Spektrums eine auf Dichtefunktionaltheorie basierende Methode verwendet (die sogenannte Transition-Potential Methode). Gängige wellenfunktionsbasierte Methoden, wie die Konfigurationswechselwirkung mit Einfachanregungen (CIS), zeigen eine starke Blauverschiebung, wenn als Referenz eine Hartree-Fock Slaterdeterminante verwendet wird. Wir zeigen, dass die Verwendung von kernnah-angeregten Determinanten sowohl das resultierende Spektrum als auch die Anregungsenergien deutlich verbessert. Des Weiteren werden auch Referenzen aus Dichtefunktionalrechnungen getestet. Zusätzlich werden auch Referenzen mit gebrochenen Besetzungszahlen für kernnahe Elektronen verwendet. In der Arbeit werden die Resultate der verschiedenen Referenzen miteinander verglichen. Es zeigt sich, dass Referenzen mit gebrochenen Besetzungszahlen das Spektrum nicht weiter verbessern. Der Einfluss der verwendeten Elektronenstrukturmethode ist eher gering.
The dissertation presents scientific results, which were worked out during December 2012 - August 2016. The work focuses on the simulation of X-ray absorption processes of several condensed phase systems. In particular, we calculated near edge X-ray absorption (NEXAFS) as well as X-ray photoelectron spectra (XPS). In both cases an incoming X-ray photon is absorbed by a molecular system. Due to the relatively high photon energy, a tightly bound core electron is excited. For XPS, this electron is promoted to high lying continuum states. The binding energy of the core electron, which is the key feature of XPS, can be calculated as the difference between the energy of the incoming photon and the measured kinetic energy of the electron. For NEXAFS spectra, the absorption probability of a photon as a function of the wavelength of the incoming radiation is measured. Both experimental methods are presented in chapter one of my thesis.
Often the experimental spectra contain a lot of resonances, which make the interpretation and analysis complicated. In such cases, quantum chemical calculations can help to understand the spectra. In chapter two the central theoretical methods are presented, which are necessary to simulate the X-ray absorption processes.
The first investigated system is graphene, which was treated with bromine plasma in order to modify the chemical and physical properties by adding bromine. The measured NEXAFS spectra of modified graphene show significant differences with respect to the spectra of the untreated surface. With the help of periodic density functional theory (DFT) calculations and simulations of spectra, it is demonstrated that physical defects are primarily responsible for the observed changes in the spectra.
Polyvinyl alcohol (PVA) is the second investigated system. We were interested in the influence of the molecular motion on the broadening of the XPS peaks. Further, we looked at the intermolecular interactions and their influence on the peak positions and broadenings. In order to accomplish this, a combination of molecular dynamics and quantum chemical methods have been used. Appropriate structures based on oligomer models were created and propagated under the influence of an (ab initio) potential. Snapshots were taken during the propagation to calculate the core electron binding energies.
In the third part of my work, Ionic Liquids have been investigated. The experiment found a very complex and complicated absorption behavior with a lot of resonances. We used cluster models, based on experimental crystallographic data, to simulate the spectra with density functional methods. Our calculations allow a comprehensive and in-depth analysis of the experimental spectra. The interpretation could be significantly extended.
In all presented systems, the so-called transition potential (TP)-DFT method based on density functional theory has been used. Common wave function based methods like configuration interaction singles (CIS) are inappropriate to calculate X-ray absorption spectra, when a Hartree-Fock reference is used. We demonstrate that, by using core-hole excited determinants as reference wave function for CIS calculations, the quality of the obtained spectra can be significantly improved. We further investigate the influence of different density functionals as well as fractional occupations to the shape and position of the resulting spectra.
urn:nbn:de:kobv:517-opus4-104844
online registration
Dissertation, Universität Potsdam, 2017
VE 5657
Keine öffentliche Lizenz: Unter Urheberrechtsschutz
Christopher Ehlert
eng
uncontrolled
quantum chemical calculations
eng
uncontrolled
XPS
eng
uncontrolled
NEXAFS
eng
uncontrolled
DFT
eng
uncontrolled
condensed phase systems
deu
uncontrolled
quantenchemische Berechnungen
deu
uncontrolled
XPS
deu
uncontrolled
NEXAFS
deu
uncontrolled
DFT
deu
uncontrolled
kondensierte Phase
Chemie und zugeordnete Wissenschaften
open_access
Institut für Chemie
Universität Potsdam
Universität Potsdam
https://publishup.uni-potsdam.de/files/10484/ehlert_diss.pdf
39441
2016
2016
eng
8654
8661
8
postprint
1
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2016-02-05
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A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids
In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC1im]+[NTf2]- and [C4C1im]+[I]-). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
urn:nbn:de:kobv:517-opus4-394417
online registration
Au-032781
Phys. Chem. Chem. Phys. (2016) Nr. 18, S. 8654-8661. - DOI: 10.1039/C5CP07434G
Christopher Ehlert
Markus Holzweber
Andreas Lippitz
Wolfgang E. S. Unger
Peter Saalfrank
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
315
eng
uncontrolled
ray absorption-spectroscopy
eng
uncontrolled
fine-structure
eng
uncontrolled
spectra
eng
uncontrolled
simulations
eng
uncontrolled
molecules
eng
uncontrolled
dynamics
eng
uncontrolled
graphene
eng
uncontrolled
surface
eng
uncontrolled
salts
Chemie und zugeordnete Wissenschaften
open_access
Institut für Chemie
Referiert
RSC
Universität Potsdam
https://publishup.uni-potsdam.de/files/39441/pmnr315_online.pdf
61286
2022
2022
eng
8516
8521
6
36
13
article
American Chemical Society
Washington, DC
1
2022-09-06
2022-09-06
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Why ultrafast photoinduced CO desorption dominates over oxidation on Ru(0001)
CO oxidation on Ru(0001) is a long-standing example of a reaction that, being thermally forbidden in ultrahigh vacuum, can be activated by femtosecond laser pulses. In spite of its relevance, the precise dynamics of the photoinduced oxidation process as well as the reasons behind the dominant role of the competing CO photodesorption remain unclear. Here we use ab initio molecular dynamics with electronic friction that account for the highly excited and nonequilibrated system created by the laser to investigate both reactions. Our simulations successfully reproduce the main experimental findings: the existence of photoinduced oxidation and desorption, the large desorption to oxidation branching ratio, and the changes in the O K-edge X-ray absorption spectra attributed to the initial stage of the oxidation process. Now, we are able to monitor in detail the ultrafast CO desorption and CO oxidation occurring in the highly excited system and to disentangle what causes the unexpected inertness to the otherwise energetically favored oxidation.
The journal of physical chemistry letters
10.1021/acs.jpclett.2c02327
36067002
1948-7185
outputup:dataSource:WoS:2022
WOS:000862128200001
Tetenoire, A; Alducin, M (corresponding author), Donostia Int Phys Ctr DIPC, Donostia San Sebastian 20018, Spain.; Tetenoire, A; Alducin, M (corresponding author), Univ Basque Country, Ctr Fis Mat CFM, MPC, CSIC, San Sebastian 20018, Spain., maite.alducin@ehu.eus
Gobierno Vasco-UPV/EHU [IT1569-22]; Deutsche Forschungsgemeinschaft; (DFG) [Sa 547-18]; Klaus Tschira Foundation; Spanish MCIN/AEI; [PID2019-107396GB-I00]
Alducin, Maite
2023-11-09T08:22:18+00:00
sword
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filename=package.tar
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CC-BY - Namensnennung 4.0 International
Auguste Tetenoire
Christopher Ehlert
Joseba Iñaki Juaristi
Peter Saalfrank
Maite Alducin
Chemie und zugeordnete Wissenschaften
Institut für Chemie
Referiert
Import
Hybrid Open-Access
7442
2014
2014
eng
14083
14095
13
postprint
1
2015-03-25
2014-05-23
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C K-edge NEXAFS spectra of graphene with physical and chemical defects
Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.
a study based on density functional theory
urn:nbn:de:kobv:517-opus4-74429
online registration
Au-006614
Physical Chemistry, Chemical Physics (2014) 16, S. 14083-14095 - DOI: 10.1039/c4cp01106f
<a href="http://publishup.uni-potsdam.de/opus4-ubp/frontdoor/index/index/docId/7441">Bibliographieeintrag der Originalveröffentlichung/Quelle</a>
Christopher Ehlert
Wolfgang E. S. Unger
Peter Saalfrank
Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
paper 173
eng
uncontrolled
absorbtion fine-structure
eng
uncontrolled
graphite
Chemie und zugeordnete Wissenschaften
open_access
Institut für Chemie
Referiert
Open Access
Universität Potsdam
https://publishup.uni-potsdam.de/files/7442/pmnr173.pdf
7441
2014
2014
eng
14083
14095
13
16
2014
article
1
--
2014-05-23
--
C K-edge NEXAFS spectra of graphene with physical and chemical defects
Recently, C K-edge Near Edge X-ray Absorption Fine Structure (NEXAFS) spectra of graphite (HOPG) surfaces have been measured for the pristine material, and for HOPG treated with either bromine or krypton plasmas (Lippitz et al., Surf. Sci., 2013, 611, L1). Changes of the NEXAFS spectra characteristic for physical (krypton) and/or chemical/physical modifications of the surface (bromine) upon plasma treatment were observed. Their molecular origin, however, remained elusive. In this work we study by density functional theory, the effects of selected point and line defects as well as chemical modifications on NEXAFS carbon K-edge spectra of single graphene layers. For Br-treated surfaces, also Br 3d X-ray Photoelectron Spectra (XPS) are simulated by a cluster approach, to identify possible chemical modifications. We observe that some of the defects related to plasma treatment lead to characteristic changes of NEXAFS spectra, similar to those in experiment. Theory provides possible microscopic origins for these changes.
physical chemistry, chemical physics : PCCP
a study based on density functional theory
1463-9076
10.1039/c4cp01106f
1463-9084
online registration
Au-006614
<a href="http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-74429">Zweitveröffentlichung als Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe ; 173</a>
Christopher Ehlert
Wolfgang E. S. Unger
Peter Saalfrank
eng
uncontrolled
absorbtion fine-structure
eng
uncontrolled
graphite
Chemie und zugeordnete Wissenschaften
Institut für Chemie
Referiert
Open Access
RSC
Universität Potsdam