TY  - JOUR
A1  - Sun, Y. -P.
A1  - Hennies, Franz
A1  - Pietzsch, Annette
A1  - Kennedy, B.
A1  - Schmitt, Thorsten
A1  - Strocov, Vladimir N.
A1  - Andersson, Joakim
A1  - Berglund, Martin
A1  - Rubensson, Jan-Erik
A1  - Aidas, K.
A1  - Gel'mukhanov, F.
A1  - Odelius, Michael
A1  - Föhlisch, Alexander
T1  - Intramolecular soft modes and intermolecular interactions in liquid acetone
JF  - Physical review : B, Condensed matter and materials physics
N2  - Resonant inelastic x-ray scattering spectra excited at the O1s(-1)pi* resonance of liquid acetone are presented. Scattering to the electronic ground state shows a resolved vibrational progression where the dominant contribution is due to the C-O stretching mode, thus demonstrating a unique sensitivity of the method to the local potential energy surface in complex molecular systems. For scattering to electronically excited states, soft vibrational modes and, to a smaller extent, intermolecular interactions give a broadening, which blurs the vibrational fine structure. It is predicted that environmental broadening is dominant in aqueous acetone.
Y1  - 2011
U6  - https://doi.org/10.1103/PhysRevB.84.132202
SN  - 1098-0121
VL  - 84
IS  - 13
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Wernet, Philippe
A1  - Kunnus, Kristjan
A1  - Schreck, Simon
A1  - Quevedo, Wilson
A1  - Kurian, Reshmi
A1  - Techert, Simone
A1  - de Groot, Frank M. F.
A1  - Odelius, Michael
A1  - Föhlisch, Alexander
T1  - Dissecting local atomic and intermolecular interactions of transition-metal ions in solution with selective X-ray spectroscopy
JF  - The journal of physical chemistry letters
N2  - Determining covalent and charge-transfer contributions to bonding in solution has remained an experimental challenge. Here, the quenching of fluorescence decay channels as expressed in dips in the L-edge X-ray spectra of solvated 3d transition-metal ions and complexes was reported as a probe. With a full set of experimental and theoretical ab initio L-edge X-ray spectra of aqueous Cr3+, including resonant inelastic X-ray scattering, we address covalency and charge transfer for this prototypical transition-metal ion in solution. We dissect local atomic effects from intermolecular interactions and quantify X-ray optical effects. We find no evidence for the asserted ultrafast charge transfer to the solvent and show that the dips are readily explained by X-ray optical effects and local atomic state dependence of the fluorescence yield. Instead, we find, besides ionic interactions, a covalent contribution to the bonding in the aqueous complex of ligand-to-metal charge-transfer character.
Y1  - 2012
U6  - https://doi.org/10.1021/jz301486u
SN  - 1948-7185
VL  - 3
IS  - 23
SP  - 3448
EP  - 3453
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Josefsson, Ida
A1  - Schreck, Simon
A1  - Quevedo, Wilson
A1  - Miedema, Piter S.
A1  - Techert, Simone
A1  - de Groot, Frank M. F.
A1  - Odelius, Michael
A1  - Wernet, Philippe
A1  - Föhlisch, Alexander
T1  - From Ligand Fields to Molecular Orbitals: Probing the Local Valence Electronic Structure of Ni2+ in Aqueous Solution with Resonant Inelastic X-ray Scattering
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - Bonding of the Ni2+(aq) complex is investigated with an unprecedented combination of resonant inelastic X-ray scattering (RIXS) measurements and ab initio calculations at the Ni L absorption edge. The spectra directly reflect the relative energies of the ligand-field and charge-transfer valence-excited states. They give element-specific access with atomic resolution to the ground-state electronic structure of the complex and allow quantification of ligand-field strength and 3d-3d electron correlation interactions in the Ni2+(aq) complex. The experimentally determined ligand-field strength is 10Dq = 1.1 eV. This and the Racah parameters characterizing 3d-3d Coulomb interactions B = 0.13 eV and C = 0.42 eV as readily derived from the measured energies match very well with the results from UV-vis spectroscopy. Our results demonstrate how L-edge RIXS can be used to complement existing spectroscopic tools for the investigation of bonding in 3d transition-metal coordination compounds in solution. The ab initio RASPT2 calculation is successfully used to simulate the L-edge RIXS spectra.
Y1  - 2013
U6  - https://doi.org/10.1021/jp4100813
SN  - 1520-6106
VL  - 117
IS  - 51
SP  - 16512
EP  - 16521
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - INPR
A1  - Föhlisch, Alexander
A1  - de Groot, F. M. F.
A1  - Odelius, Michael
A1  - Techert, Simone
A1  - Wernet, P.
T1  - Comment on "state-dependent electron delocalization dynamics at the solute-solvent interface: soft-x-ray absorption spectroscopy and lambda b initio calculations"
T2  - Physical review letters
Y1  - 2014
U6  - https://doi.org/10.1103/PhysRevLett.112.129302
SN  - 0031-9007
SN  - 1079-7114
VL  - 112
IS  - 12
PB  - American Physical Society
CY  - College Park
ER  - 
TY  - JOUR
A1  - Wernet, Philippe
A1  - Kunnus, Kristjan
A1  - Josefsson, Ida
A1  - Rajkovic, Ivan
A1  - Quevedo, Wilson
A1  - Beye, Martin
A1  - Schreck, Simon
A1  - Gruebel, S.
A1  - Scholz, Mirko
A1  - Nordlund, Dennis
A1  - Zhang, Wenkai
A1  - Hartsock, Robert W.
A1  - Schlotter, William F.
A1  - Turner, Joshua J.
A1  - Kennedy, Brian
A1  - Hennies, Franz
A1  - de Groot, Frank M. F.
A1  - Gaffney, Kelly J.
A1  - Techert, Simone
A1  - Odelius, Michael
A1  - Föhlisch, Alexander
T1  - Orbital-specific mapping of the ligand exchange dynamics of Fe(CO)(5) in solution
JF  - Nature : the international weekly journal of science
N2  - Transition-metal complexes have long attracted interest for fundamental chemical reactivity studies and possible use in solar energy conversion(1,2). Electronic excitation, ligand loss from the metal centre, or a combination of both, creates changes in charge and spin density at the metal site(3-11) that need to be controlled to optimize complexes for photocatalytic hydrogen production(8) and selective carbon-hydrogen bond activation(9-11). An understanding at the molecular level of how transition-metal complexes catalyse reactions, and in particular of the role of the short-lived and reactive intermediate states involved, will be critical for such optimization. However, suitable methods for detailed characterization of electronic excited states have been lacking. Here we show, with the use of X-ray laser-based femtosecond-resolution spectroscopy and advanced quantum chemical theory to probe the reaction dynamics of the benchmark transition-metal complex Fe(CO)(5) in solution, that the photo-induced removal of CO generates the 16-electron Fe(CO)(4) species, a homogeneous catalyst(12,13) with an electron deficiency at the Fe centre(14,15), in a hitherto unreported excited singlet state that either converts to the triplet ground state or combines with a CO or solvent molecule to regenerate a penta-coordinated Fe species on a sub-picosecond timescale. This finding, which resolves the debate about the relative importance of different spin channels in the photochemistry of Fe(CO)(5) (refs 4, 16-20), was made possible by the ability of femtosecond X-ray spectroscopy to probe frontier-orbital interactions with atom specificity. We expect the method to be broadly applicable in the chemical sciences, and to complement approaches that probe structural dynamics in ultrafast processes.
Y1  - 2015
U6  - https://doi.org/10.1038/nature14296
SN  - 0028-0836
SN  - 1476-4687
VL  - 520
IS  - 7545
SP  - 78
EP  - 81
PB  - Nature Publ. Group
CY  - London
ER  - 
TY  - JOUR
A1  - Premont-Schwarz, Mirabelle
A1  - Schreck, Simon
A1  - Iannuzzi, Marcella
A1  - Nibbering, Erik T. J.
A1  - Odelius, Michael
A1  - Wernet, Philippe
T1  - Correlating Infrared and X-ray Absorption Energies for Molecular-Level Insight into Hydrogen Bond Making and Breaking in Solution
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - While ubiquitous, the making and breaking of hydrogen bonds in solution is notoriously difficult to study due to the associated complex changes of nuclear and electronic structures. With the aim to reduce the according uncertainty in correlating experimental observables and hydrogen-bond configurations, we combine the information from proximate methods to study the N-H center dot center dot center dot O hydrogen bond in solution. We investigate hydrogen-bonding of the N-H group of N-methylaniline with oxygen from liquid DMSO and acetone with infrared spectra in the N-H stretching region and X-ray absorption spectra at the N K-edge. We experimentally observe blue shifts of the infrared stretching band and an X-ray absorption pre-edge peak when going from DMSO to acetone. With ab initio molecular dynamics simulations and calculated spectra, we qualitatively reproduce the experimental observables but we do not reach quantitative agreement with experiment. The infrared spectra support the notion of weakening the N-H center dot center dot center dot O hydrogen bond from DMSO to acetone. However, we fail to theoretically reproduce the measured shift of the X-ray absorption pre-edge peak. We discuss possible shortcomings of the simulation models and spectrum calculations. Common features and distinct differences with the O-H center dot center dot center dot O hydrogen bond are highlighted, and the implications for monitoring hydrogen-bond breaking in solution are discussed.
Y1  - 2015
U6  - https://doi.org/10.1021/acs.jpcb.5b02954
SN  - 1520-6106
VL  - 119
IS  - 25
SP  - 8115
EP  - 8124
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Josefsson, Ida
A1  - Rajkovic, Ivan
A1  - Schreck, Simon
A1  - Quevedo, Wilson
A1  - Beye, Martin
A1  - Grübel, Sebastian
A1  - Scholz, Mirko
A1  - Nordlund, Dennis
A1  - Zhang, Wenkai
A1  - Hartsock, Robert W.
A1  - Gaffney, Kelly J.
A1  - Schlotter, William F.
A1  - Turner, Joshua J.
A1  - Kennedy, Brian
A1  - Hennies, Franz
A1  - Techert, Simone
A1  - Wernet, Philippe
A1  - Odelius, Michael
A1  - Föhlisch, Alexander
T1  - Anti-Stokes resonant x-ray Raman scattering for atom specific and excited state selective dynamics
JF  - NEW JOURNAL OF PHYSICS
N2  - Ultrafast electronic and structural dynamics of matter govern rate and selectivity of chemical reactions, as well as phase transitions and efficient switching in functional materials. Since x-rays determine electronic and structural properties with elemental, chemical, orbital and magnetic selectivity, short pulse x-ray sources have become central enablers of ultrafast science. Despite of these strengths, ultrafast x-rays have been poor at picking up excited state moieties from the unexcited ones. With time-resolved anti-Stokes resonant x-ray Raman scattering (AS-RXRS) performed at the LCLS, and ab initio theory we establish background free excited state selectivity in addition to the elemental, chemical, orbital and magnetic selectivity of x-rays. This unparalleled selectivity extracts low concentration excited state species along the pathway of photo induced ligand exchange of Fe(CO)(5) in ethanol. Conceptually a full theoretical treatment of all accessible insights to excited state dynamics with AS-RXRS with transform-limited x-ray pulses is given-which will be covered experimentally by upcoming transform-limited x-ray sources.
KW  - ultrafast photochemistry
KW  - excited state selectivity
KW  - anti-Stokes resonant x-ray raman scattering
KW  - free electron lasers
KW  - resonant inelastic x-ray scattering
Y1  - 2016
U6  - https://doi.org/10.1088/1367-2630/18/10/103011
SN  - 1367-2630
VL  - 18
PB  - IOP Publ. Ltd.
CY  - Bristol
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Josefsson, I.
A1  - Rajkovic, Ivan
A1  - Schreck, Simon
A1  - Quevedo, Wilson
A1  - Beye, Martin
A1  - Weniger, C.
A1  - Gruebel, S.
A1  - Scholz, M.
A1  - Nordlund, D.
A1  - Zhang, W.
A1  - Hartsock, R. W.
A1  - Gaffney, K. J.
A1  - Schlotter, W. F.
A1  - Turner, J. J.
A1  - Kennedy, B.
A1  - Hennies, F.
A1  - de Groot, F. M. F.
A1  - Techert, S.
A1  - Odelius, Michael
A1  - Wernet, Ph.
A1  - Föhlisch, Alexander
T1  - Identification of the dominant photochemical pathways and mechanistic insights to the ultrafast ligand exchange of Fe(CO)(5) to Fe(CO)(4)EtOH
JF  - Structural dynamics
N2  - We utilized femtosecond time-resolved resonant inelastic X-ray scattering and ab initio theory to study the transient electronic structure and the photoinduced molecular dynamics of a model metal carbonyl photocatalyst Fe(CO)(5) in ethanol solution. We propose mechanistic explanation for the parallel ultrafast intra-molecular spin crossover and ligation of the Fe(CO)(4) which are observed following a charge transfer photoexcitation of Fe(CO)(5) as reported in our previous study [ Wernet et al., Nature 520, 78 (2015)]. We find that branching of the reaction pathway likely happens in the (1)A(1) state of Fe(CO)(4). A sub-picosecond time constant of the spin crossover from B-1(2) to B-3(2) is rationalized by the proposed B-1(2) -> (1)A(1) -> B-3(2) mechanism. Ultrafast ligation of the B-1(2) Fe(CO)(4) state is significantly faster than the spin-forbidden and diffusion limited ligation process occurring from the B-3(2) Fe(CO)(4) ground state that has been observed in the previous studies. We propose that the ultrafast ligation occurs via B-1(2) -> (1)A(1) -> (1)A'Fe(CO)(4)EtOH pathway and the time scale of the (1)A(1) Fe(CO)(4) state ligation is governed by the solute-solvent collision frequency. Our study emphasizes the importance of understanding the interaction of molecular excited states with the surrounding environment to explain the relaxation pathways of photoexcited metal carbonyls in solution. (C) 2016 Author(s).
Y1  - 2016
U6  - https://doi.org/10.1063/1.4941602
SN  - 2329-7778
VL  - 3
PB  - American Institute of Physics
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kunnus, Kristjan
A1  - Zhang, Wenkai
A1  - Delcey, Mickael G.
A1  - Pinjari, Rahul V.
A1  - Miedema, Piter S.
A1  - Schreck, Simon
A1  - Quevedo, Wilson
A1  - Schröder, Henning
A1  - Föhlisch, Alexander
A1  - Gaffney, Kelly J.
A1  - Lundberg, Marcus
A1  - Odelius, Michael
A1  - Wernet, Philippe
T1  - Viewing the Valence Electronic Structure of Ferric and Ferrous Hexacyanide in Solution from the Fe and Cyanide Perspectives
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - The valence-excited states of ferric and ferrous hexacyanide ions in aqueous solution were mapped by resonant inelastic X-ray scattering (RIXS) at the Fe L-2,L-3 and N K edges. Probing of both the central Fe and the ligand N atoms enabled identification of the metal-and ligand-centered excited states, as well as ligand-to-metal and metal-to-ligand charge-transfer excited states. Ab initio calculations utilizing the RASPT2 method were used to simulate the Fe L-2,L-3-edge RIXS spectra and enabled quantification of the covalencies of both occupied and empty orbitals of pi and sigma symmetry. We found that pi back-donation in the ferric complex is smaller than that in the ferrous complex. This is evidenced by the relative amounts of Fe 3d character in the nominally 2 pi CN- molecular orbital of 7% and 9% in ferric and ferrous hexacyanide, respectively. Utilizing the direct sensitivity of Fe L-3-edge RIXS to the Fe 3d character in the occupied molecular orbitals, we also found that the donation interactions are dominated by sigma bonding. The latter was found to be stronger in the ferric complex, with an Fe 3d contribution to the nominally 5 sigma CN- molecular orbitals of 29% compared to 20% in the ferrous complex. These results are consistent with the notion that a higher charge at the central metal atom increases donation and decreases back-donation.
Y1  - 2016
U6  - https://doi.org/10.1021/acs.jpcb.6b04751
SN  - 1520-6106
VL  - 120
SP  - 7182
EP  - 7194
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Wernet, Philippe
A1  - Leitner, T.
A1  - Josefsson, Ida
A1  - Mazza, T.
A1  - Miedema, P. S.
A1  - Schroder, H.
A1  - Beye, Martin
A1  - Kunnus, K.
A1  - Schreck, S.
A1  - Radcliffe, P.
A1  - Dusterer, S.
A1  - Meyer, M.
A1  - Odelius, Michael
A1  - Fohlisch, Alexander
T1  - Communication: Direct evidence for sequential dissociation of gas-phase Fe(CO)(5) via a singlet pathway upon excitation at 266 nm
JF  - The journal of chemical physics : bridges a gap between journals of physics and journals of chemistr
N2  - We prove the hitherto hypothesized sequential dissociation of Fe(CO)(5) in the gas phase upon photoexcitation at 266 nm via a singlet pathway with time-resolved valence and core-level photoelectron spectroscopy with an x-ray free-electron laser. Valence photoelectron spectra are used to identify free CO molecules and to determine the time constants of stepwise dissociation to Fe(CO)(4) within the temporal resolution of the experiment and further to Fe(CO)(3) within 3 ps. Fe 3p core-level photoelectron spectra directly reflect the singlet spin state of the Fe center in Fe(CO)(5), Fe(CO)(4), and Fe(CO)(3) showing that the dissociation exclusively occurs along a singlet pathway without triplet-state contribution. Our results are important for assessing intra- and intermolecular relaxation processes in the photodissociation dynamics of the prototypical Fe(CO)(5) complex in the gas phase and in solution, and they establish time-resolved core-level photoelectron spectroscopy as a powerful tool for determining the multiplicity of transition metals in photochemical reactions of coordination complexes. Published by AIP Publishing.
Y1  - 2017
U6  - https://doi.org/10.1063/1.4984774
SN  - 0021-9606
SN  - 1089-7690
VL  - 146
PB  - American Institute of Physics
CY  - Melville
ER  -