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Fuss W.,Max Planck Institute of Quantum Optics | Robertson E.G.,La Trobe University | Medcraft C.,Monash University | Medcraft C.,Max Planck Institute For Struktur Und Dynamik Der Materie | Appadoo D.R.T.,Australian Synchrotron
Journal of Physical Chemistry A | Year: 2014

Compared to ethylene and its nonfluorinated derivatives, C 2F4 is peculiar in many reactions. It very easily adds to radicals and prefers formation of four-membered rings over Diels-Alder reactions. This has been rationalized by the preference of fluorine for carbon sp3 hybridization, which is possible on opening of the double bond. Another property, the thermal dissociation of the C=C bond, has been explained by the stabilization of the product (CF2) by back-bonding. Here, it is attempted to correlate such properties with vibrational constants, in particular for C=C stretching and twisting and for carbon pyramidalization. The only force constant found to be lowered compared to ethylene is that for trans pyramidalization (ν8), and CC bond softening on ν8 distortion is indicated by the conspicuously large magnitude of anharmonic constant, x18. Both observations can be rationalized by a valence-bond model that predicts a trans bent structure on weakening the CC bond. Conclusions are drawn about the dissociation path and peculiarities of the potential. Other anharmonicities, both experimental and calculated and some in 12C13CF4 and 13C2F 4, are also discussed. In particular some strong Fermi resonances are identified and their effects accounted for. © 2014 American Chemical Society.

Eggert D.,Max Planck Institute For Struktur Und Dynamik Der Materie | Eggert D.,Heinrich Pette Institute | Reimer R.,Heinrich Pette Institute
BioSpektrum | Year: 2015

The recently introduced sub-diffraction light microscopy techniques (STORM, STED, PALM etc.) are all based on the fluorescence phenomenon. However, the common drawback of fluorescence-based methods is the lack of structural information about the unlabeled environment. Correlating super-resolution images with structural information obtained by transmitted light or electron microscopy leads to a better interpretation of super-resolution data and provides a more complete view on any given problem. © 2015, Springer-Verlag Berlin Heidelberg.

Patterson D.,Harvard University | Schnell M.,Max Planck Institute For Struktur Und Dynamik Der Materie | Schnell M.,Center for Free Electronic Laser Science
Physical Chemistry Chemical Physics | Year: 2014

Chirality plays a fundamental role in the activity of biological molecules and broad classes of chemical reactions. The chemistry of life is built almost exclusively on left-handed amino acids and right-handed sugars, a phenomenon known as "homochirality of life". Furthermore, most drugs developed in the last decade are of specified chirality. Thus, fast and reliable methods that can differentiate molecules of different handedness, determine the enantiomeric excess of even molecular mixtures, and allow for an unambiguous determination of molecular handedness are of great interest, in particular with respect to complex mixtures. In this perspective article, we discuss the recent developments, with an emphasis on modern spectroscopic methods using gas-phase samples, such as photoelectron circular dichroism, Coulomb explosion imaging, and microwave three-wave mixing. © 2014 the Partner Organisations.

Brumme T.,CNRS Institute of Mineralogy, Materials Physics and Cosmochemistry | Brumme T.,Max Planck Institute For Struktur Und Dynamik Der Materie | Calandra M.,CNRS Institute of Mineralogy, Materials Physics and Cosmochemistry | Mauri F.,University of Rome La Sapienza
Physical Review B - Condensed Matter and Materials Physics | Year: 2016

The transition-metal dichalcogenides have attracted a lot of attention as a possible stepping-stone toward atomically thin and flexible field-effect transistors. One key parameter to describe the charge transport is the time between two successive scattering events - the transport scattering time. In a recent report, we have shown that it is possible to use density functional theory to obtain the band structure of two-dimensional semiconductors in the presence of field effect doping. Here, we report a simple method to extract the scattering time from the experimental conductivity and from the knowledge of the band structure. We apply our approach to monolayers and multilayers of MoS2, MoSe2, MoTe2, WS2, and WSe2 in the presence of a gate. In WS2, for which accurate measurements of mobility have been published, we find that the scattering time is inversely proportional to the density of states at the Fermi level. Finally, we show that it is possible to identify the critical doping at which different valleys start to be occupied from the doping dependence of the conductivity. © 2016 American Physical Society.

Drayna G.K.,Harvard University | Hallas C.,Harvard University | Wang K.,Harvard University | Domingos S.R.,Max Planck Institute For Struktur Und Dynamik Der Materie | And 4 more authors.
Angewandte Chemie - International Edition | Year: 2016

Cooling molecules in the gas phase is important for precision spectroscopy, cold molecule physics, and physical chemistry. Measurements of conformational relaxation cross sections shed important light on potential energy surfaces and energy flow within a molecule. However, gas-phase conformational cooling has not been previously observed directly. In this work, we directly observe conformational dynamics of 1,2-propanediol in cold (6 K) collisions with atomic helium using microwave spectroscopy and buffer-gas cooling. Precise knowledge and control of the collisional environment in the buffer-gas allows us to measure the absolute collision cross-section for conformational relaxation. Several conformers of 1,2-propanediol are investigated and found to have relaxation cross-sections with He ranging from σ=4.7(3.0)×10-18 cm2 to σ>5×10-16 cm2. Our method is applicable to a broad class of molecules and could be used to provide information about the potential energy surfaces of previously uninvestigated molecules. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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