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- ItemSingle Molecule Magnetism with Strong Magnetic Anisotropy and Enhanced Dy∙∙∙Dy Coupling in Three Isomers of Dy-Oxide Clusterfullerene Dy2O@C82(Chichester : John Wiley and Sons Ltd, 2019) Yang, W.; Velkos, G.; Liu, F.; Sudarkova, S.M.; Wang, Y.; Zhuang, J.; Zhang, H.; Li, X.; Zhang, X.; Büchner, B.; Avdoshenko, S.M.; Popov, A.A.; Chen, N.A new class of single-molecule magnets (SMMs) based on Dy-oxide clusterfullerenes is synthesized. Three isomers of Dy2O@C82 with Cs(6), C3v(8), and C2v(9) cage symmetries are characterized by single-crystal X-ray diffraction, which shows that the endohedral Dy−(µ2-O)−Dy cluster has bent shape with very short Dy−O bonds. Dy2O@C82 isomers show SMM behavior with broad magnetic hysteresis, but the temperature and magnetization relaxation depend strongly on the fullerene cage. The short Dy−O distances and the large negative charge of the oxide ion in Dy2O@C82 result in the very strong magnetic anisotropy of Dy ions. Their magnetic moments are aligned along the Dy−O bonds and are antiferromagnetically (AFM) coupled. At low temperatures, relaxation of magnetization in Dy2O@C82 proceeds via the ferromagnetically (FM)-coupled excited state, giving Arrhenius behavior with the effective barriers equal to the AFM-FM energy difference. The AFM-FM energy differences of 5.4–12.9 cm−1 in Dy2O@C82 are considerably larger than in SMMs with {Dy2O2} bridges, and the Dy∙∙∙Dy exchange coupling in Dy2O@C82 is the strongest among all dinuclear Dy SMMs with diamagnetic bridges. Dy-oxide clusterfullerenes provide a playground for the further tuning of molecular magnetism via variation of the size and shape of the fullerene cage.
- ItemTowards multiple readout application of plasmonic arrays(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2011) Cialla, D.; Weber, K.; Böhme, R.; Hübner, U.; Schneidewind, H.; Zeisberger, M.; Mattheis, R.; Möller, R.; Popp, J.In order to combine the advantages of fluorescence and surface-enhanced Raman spectroscopy (SERS) on the same chip platform, a nanostructured gold surface with a unique design, allowing both the sensitive detection of fluorescence light together with the specific Raman fingerprint of the fluorescent molecules, was established. This task requires the fabrication of plasmonic arrays that permit the binding of molecules of interest at different distances from the metallic surface. The most efficient SERS enhancement is achieved for molecules directly adsorbed on the metallic surface due to the strong field enhancement, but where, however, the fluorescence is quenched most efficiently. Furthermore, the fluorescence can be enhanced efficiently by careful adjustment of the optical behavior of the plasmonic arrays. In this article, the simultaneous application of SERS and fluorescence, through the use of various gold nanostructured arrays, is demonstrated by the realization of a DNA detection scheme. The results shown open the way to more flexible use of plasmonic arrays in bioanalytics.
- ItemRecent advances in single molecule magnetism of dysprosium-metallofullerenes(Cambridge : Royal Society of Chemistry, 2019) Spree, L.; Popov, A.A.This article outlines the magnetic properties of single molecule magnets based on Dy-encapsulating endohedral metallofullerenes. The factors that govern these properties, such as the influence of different non-metal species in clusterfullerenes, the cage size, and cage isomerism are discussed, as well as the recent successful isolation of dimetallofullerenes with unprecedented magnetic properties. Finally, recent advances towards the organization of endohedral metallofullerenes in 1D, 2D, and 3D ordered structures with potential for devices are reviewed.
- ItemTuning the magneto-optical response of TbPc2 single molecule magnets by the choice of the substrate(London [u.a.] : RSC, 2015) Robaschik, Peter; Fronk, Michael; Toader, Marius; Klyatskaya, Svetlana; Ganss, Fabian; Siles, Pablo F.; Schmidt, Oliver G.; Albrecht, Manfred; Hietschold, Michael; Ruben, Mario; Zahn, Dietrich R.T.; Salvan, GeorgetaIn this work, we investigated the magneto-optical response of thin films of TbPc2 on substrates which are relevant for (spin) organic field effect transistors (SiO2) or vertical spin valves (Co) in order to explore the possibility of implementing TbPc2 in magneto-electronic devices, the functionality of which includes optical reading. The optical and magneto-optical properties of TbPc2 thin films prepared by organic molecular beam deposition (OMBD) on silicon substrates covered with native oxide were investigated by variable angle spectroscopic ellipsometry (VASE) and magneto-optical Kerr effect (MOKE) spectroscopy at room temperature. The magneto-optical activity of the TbPc2 films can be significantly enhanced by one to two orders of magnitude upon changing the molecular orientation (from nearly standing molecules on SiO2/Si substrates to nearly lying molecules on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) templated SiO2/Si substrates) or by using metallic ferromagnetic substrates (Co).
- ItemFull-dimensional treatment of short-time vibronic dynamics in a molecular high-order-harmonic-generation process in methane(College Park, Md : APS, 2017) Patchkovskii, Serguei; Schuurman, Michael S.We present derivation and implementation of the multiconfigurational strong-field approximation with Gaussian nuclear wave packets (MC-SFA-GWP) - a version of the molecular strong-field approximation which treats all electronic and nuclear degrees of freedom, including their correlations, quantum mechanically. The technique allows realistic simulation of high-order-harmonic emission in polyatomic molecules without invoking reduced-dimensionality models for the nuclear motion or the electronic structure. We use MC-SFA-GWP to model isotope effects in high-order-harmonic-generation (HHG) spectroscopy of methane. The HHG emission in this molecule transiently involves the strongly vibronically coupled F22 electronic state of the CH4+ cation. We show that the isotopic HHG ratio in methane contains signatures of (a) field-free vibronic dynamics at the conical intersection (CI); (b) resonant features in the recombination cross sections; (c) laser-driven bound-state dynamics; as well as (d) the well-known short-time Gaussian decay of the emission. We assign the intrinsic vibronic feature (a) to a relatively long-lived (≥4 fs) vibronic wave packet of the singly excited ν4 (t2) and ν2 (e) vibrational modes, strongly coupled to the components of the F22 electronic state. We demonstrate that these physical effects differ in their dependence on the wavelength, intensity, and duration of the driving pulse, allowing them to be disentangled. We thus show that HHG spectroscopy provides a versatile tool for exploring both conical intersections and resonant features in photorecombination matrix elements in the regime not easily accessible with other techniques.
- ItemCoulomb explosion of diatomic molecules in intense XUV fields mapped by partial covariance(Bristol : Institute of Physics Publishing, 2013) Kornilov, O.; Eckstein, M.; Rosenblatt, M.; Schulz, C.P.; Motomura, K.; Rouzée, A.; Klei, J.; Foucar, L.; Siano, M.; Lübcke, A.; Schapper, F.; Johnsson, P.; Holland, D.M.P.; Schlathölter, T.; Marchenko, T.; Düsterer, S.; Ueda, K.; Vrakking, M.J.J.; Frasinski, L.J.Single-shot time-of-flight spectra for Coulomb explosion of N2 and I2 molecules have been recorded at the Free Electron LASer in Hamburg (FLASH) and have been analysed using a partial covariance mapping technique. The partial covariance analysis unravels a detailed picture of all significant Coulomb explosion pathways, extending up to the N 4+-N5+ channel for nitrogen and up to the I 8+-I9+ channel for iodine. The observation of the latter channel is unexpected if only sequential ionization processes from the ground state ions are considered. The maximum kinetic energy release extracted from the covariance maps for each dissociation channel shows that Coulomb explosion of nitrogen molecules proceeds much faster than that of the iodine. The N 2 ionization dynamics is modelled using classical trajectory simulations in good agreement with the outcome of the experiments. The results suggest that covariance mapping of the Coulomb explosion can be used to measure the intensity and pulse duration of free-electron lasers.
- ItemMolecular above-threshold ionization spectra as an evidence of the three-point interference of electron wave packets(Bristol : IOP Publ., 2015) Hasović, Elvedin; Milošević, Dejan B.; Gazibegović-Busuladži, Azra; Čerkić, Aner; Busuladžić, MustafaWe consider high-order above-threshold ionization (HATI) of polyatomic molecules ionized by a strong linearly polarized laser field. Improved molecular strong-field approximation by which the HATI process on polyatomic molecular species can be described is developed. Using this theory we calculate photoelectron angular-energy spectra for different triatomic molecules. Special attention is devoted to the minima that are observed in the calculated high-energy electron spectra of the ozone and carbon dioxide molecules. A key difference between these minima and minima that are observed in the corresponding spectra of diatomic molecules are presented.
- ItemStrong field ionization of small hydrocarbon chains with full 3D momentum analysis(Bristol : IOP Publ., 2015) Schulz, Claus Peter; Birkner, Sascha; Furch, Federico J.; Anderson, Alexandria; Mikosch, Jochen; Schell, Felix; Vrakking, Marc J. J.Strong field ionization of small hydrocarbon chains is studied in a kinematic complete experiment using a reaction microscope. By coincidence detection of ions and electrons different ionization continua populated during the ionization process are identified. In addition, photoelectron momentum distributions from laser-aligned molecules allow to characterize the electron wavepackets emerging from different Dyson orbitals.
- ItemPhotodissociation of aligned CH3I and C6H3F2I molecules probed with time-resolved Coulomb explosion imaging by site-selective extreme ultraviolet ionization(Melville, NY : AIP Publishing LLC, 2018) Amini, Kasra; Savelyev, Evgeny; Brauße, Felix; Berrah, Nora; Bomme, Cédric; Brouard, Mark; Burt, Michael; Christensen, Lauge; Düsterer, Stefan; Erk, Benjamin; Höppner, Hauke; Kierspel, Thomas; Krecinic, Faruk; Lauer, Alexandra; Lee, Jason W. L.; Müller, Maria; Müller, Erland; Mullins, Terence; Redlin, Harald; Schirmel, Nora; Thøgersen, Jan; Techert, Simone; Toleikis, Sven; Treusch, Rolf; Trippel, Sebastian; Ulmer, Anatoli; Vallance, Claire; Wiese, Joss; Johnsson, Per; Küpper, Jochen; Rudenko, Artem; Rouzée, Arnaud; Stapelfeldt, Henrik; Rolles, Daniel; Boll, RebeccaWe explore time-resolved Coulomb explosion induced by intense, extreme ultraviolet (XUV) femtosecond pulses from a free-electron laser as a method to image photo-induced molecular dynamics in two molecules, iodomethane and 2,6-difluoroiodobenzene. At an excitation wavelength of 267 nm, the dominant reaction pathway in both molecules is neutral dissociation via cleavage of the carbon-iodine bond. This allows investigating the influence of the molecular environment on the absorption of an intense, femtosecond XUV pulse and the subsequent Coulomb explosion process. We find that the XUV probe pulse induces local inner-shell ionization of atomic iodine in dissociating iodomethane, in contrast to non-selective ionization of all photofragments in difluoroiodobenzene. The results reveal evidence of electron transfer from methyl and phenyl moieties to a multiply charged iodine ion. In addition, indications for ultrafast charge rearrangement on the phenyl radical are found, suggesting that time-resolved Coulomb explosion imaging is sensitive to the localization of charge in extended molecules.
- ItemPerspective: Structure and ultrafast dynamics of biomolecular hydration shells(Melville, NY : AIP Publishing LLC, 2017) Laage, Damien; Elsaesser, Thomas; Hynes, James T.The structure and function of biomolecules can be strongly influenced by their hydration shells. A key challenge is thus to determine the extent to which these shells differ from bulk water, since the structural fluctuations and molecular excitations of hydrating water molecules within these shells can cover a broad range in both space and time. Recent progress in theory, molecular dynamics simulations, and ultrafast vibrational spectroscopy has led to new and detailed insight into the fluctuations of water structure, elementary water motions, and electric fields at hydrated biointerfaces. Here, we discuss some central aspects of these advances, focusing on elementary molecular mechanisms and processes of hydration on a femto-to picosecond time scale, with some special attention given to several issues subject to debate.