From Torsional Spectra to Hamiltonians and Dynamics: Effects of Coupled Bright and Dark States of 9-(N-Carbazolyl) Anthracene

The torsional dynamics of the 9-(N-carbazolyl)-anthracene (C9A) molecule is investigated by means of time-independent (1) and time-dependent (2) quantum-mechanical simulations in a diabatic representation. The study includes effects of surface crossing of the bright S1 state with a dark state. The intensity pattern of the S0->S1 fluorescence excitation spectrum is used to fit an effective one-dimensional Hamiltonian with a single-minimum potential for the dark state together with diabatic couplings to the double well potential of the bright state. Based on this Hamiltonian, first predictions for a pump-probe scheme are made. In the pump process the molecules are excited to the S1 state followed by competing torsions in the bright state and diabatic curve crossings to the dark state, depending on the pump frequency. Assuming the probe process to be an ionization from the bright state, the interfering effects of the dark state on the dynamics in the bright state can be monitored in a directly time-dependent way on a fs - ps time scale

Effect of Rotations and Shape Resonances on Photoassociation and Photoacceleration by Ultrashort Infrared Laser Pulses

A quantum dynamical description of an atomic collision pair interacting with the electric field of a short infrared laser pulse is developed. Inelastic processes in the electronic ground state are due to stimulated emission resulting in photoassociation, or absorption leading to photoacceleration. A perturbative approach based on a state space representation is compared with a numerical treatment using a grid representation in coordinate space. Special emphasis is on the role of rotations and, in particular, of shape resonances. It is shown that these quasibound states which are supported by the centrifugal barrier (for J> 0) can be used as initial states to effectively populate a selected bound state with specific vibrational and rotational quantum number (photoassociation), or a partial wave of a scattering state with defined energy and rotational quantum number (photoacceleration). Simulations are carried out for the prototype H + Cl collision pair. Also the effect of averaging over initial conditions (velocity, angular momenta) is investigated for a supersonic beam experiment. For a narrow velocity distribution, we predict the presence of a resonance structure of the association and acceleration probability as a function of the mean collision energy

Quantum Dynamical Aspects of Rotationally and Vibrationally Mediated Photochemistry in Matrices and at Surfaces: HCl/DCl in Ar, and NH3/ND3 at Cu(111)

In this paper, we investigate two extensions of the concept of vibrationally mediated chemistry, from small molecules in the gas phase to small molecules in matrices and at surfaces. Exemplarily, we consider the systems HCl/DCl in Ar, and NH3/ND3 at Cu (111). The transition from isolated systems to the condensed phase calls for new quantum dynamical techniques, and it allows to predict new phenomena. For the case of matrix isolation, we propagate three-dimensional wavepackets representing photodissociated H- or D-atoms which penetrate from the initial cage into the lattice provided by the matrix. The cage exit probabilities are found to depend not only on the initial vibrational, but also on the rotational states, due to the environmental (Oh) symmetry provided by the (fcc) lattice of the matrix. As a consequence, we suggest the extension from vibrationally to rotationally, or rovibrationally mediated chemistry for matrix isolated molecules. For the case of molecules at surfaces, we adopt Gadzuk's jumping wavepacket plus incoherent averaging scheme, applied to an extended two-dimensional Antoniewicz-type model for the surface-molecule bond plus the vibrational coordinate which lends itself to preferential vibrational excitation, (here the umbrella mode of ammonia). The desorption depends selectively on the initial vibrational state. As a consequence, we suggest the extension of traditional desorption induced by electronic transitions DIET to a vibrationally mediated IR+UV DIET scheme which may be used e.g. for enrichment of specific isotopomers at surfaces

Non-invasive diagnostics in fossils - Magnetic Resonance Imaging of pathological belemnites

For more than a decade, Magnetic Resonance Imaging (MRI) has been routinely employed in clinical diagnostics because it allows non-invasive studies of anatomical structures and physiological processes <I>in vivo</I> and to differentiate between healthy and pathological states, particularly of soft tissue. Here, we demonstrate that MRI can likewise be applied to fossilized biological samples and help in elucidating paleopathological and paleoecological questions: Five anomalous guards of Jurassic and Cretaceous belemnites are presented along with putative paleopathological diagnoses directly derived from 3D MR images with microscopic resolution. <I>Syn vivo</I> deformities of both the mineralized internal rostrum and the surrounding former soft tissue can be traced back in part to traumatic events of predator-prey-interactions, and partly to parasitism. Besides, evidence is presented that the frequently observed anomalous apical collar might be indicative of an inflammatory disease. These findings highlight the potential of Magnetic Resonance techniques for further paleontological applications

Three-dimensional Magnetic Resonance Imaging of fossils across taxa

The frequency of life forms in the fossil record is largely determined by the extent to which they were mineralised at the time of their death. In addition to mineral structures, many fossils nonetheless contain detectable amounts of residual water or organic molecules, the analysis of which has become an integral part of current palaeontological research. The methods available for this sort of investigations, though, typically require dissolution or ionisation of the fossil sample or parts thereof, which is an issue with rare taxa and outstanding materials like pathological or type specimens. In such cases, non-destructive techniques could provide a valuable methodological alternative. While Computed Tomography has long been used to study palaeontological specimens, a number of complementary approaches have recently gained ground. These include Magnetic Resonance Imaging (MRI) which had previously been employed to obtain three-dimensional images of pathological belemnites non-invasively on the basis of intrinsic contrast. The present study was undertaken to investigate whether &lt;sup&gt;1&lt;/sup&gt;H MRI can likewise provide anatomical information about non-pathological belemnites and specimens of other fossil taxa. To this end, three-dimensional MR image series were acquired from intact non-pathological invertebrate, vertebrate and plant fossils. At routine voxel resolutions in the range of several dozens to some hundreds of micrometers, these images reveal a host of anatomical details and thus highlight the potential of MR techniques to effectively complement existing methodological approaches for palaeontological investigations in a wide range of taxa. As for the origin of the MR signal, relaxation and diffusion measurements as well as &lt;sup&gt;1&lt;/sup&gt;H and &lt;sup&gt;13&lt;/sup&gt;C MR spectra acquired from a belemnite suggest intracrystalline water or hydroxyl groups, rather than organic residues

A Reflection Principle for the Control of Molecular Photodissociation in Solids: Model Simulation for F2 in Ar

Laser pulse induced photodissociation of molecules in rare gas solids is investigated by representative quantum wavepackets or classical trajectories which are directed towards, or away from cage exits, yielding dominant photodissociation into different neighbouring cages. The directionality is determined by a sequence of reflections inside the relief provided by the slopes of the potential energy surface of the excited system, which in turn depend on the initial preparation of the matrix isolated system, e.g. by laser pulses with different frequencies or by vibrational pre-excitation of the cage atoms. This reflection principle is demonstrated for a simple, two-dimensional model of F2 in Ar

Global turbulence simulations of the tokamak edge region with GRILLIX

Turbulent dynamics in the scrape-off layer (SOL) of magnetic fusion devices is intermittent with large fluctuations in density and pressure. Therefore, a model is required that allows perturbations of similar or even larger magnitude to the time-averaged background value. The fluid-turbulence code GRILLIX is extended to such a global model, which consistently accounts for large variation in plasma parameters. Derived from the drift reduced Braginskii equations, the new GRILLIX model includes electromagnetic and electron-thermal dynamics, retains global parametric dependencies and the Boussinesq approximation is not applied. The penalisation technique is combined with the flux-coordinate independent (FCI) approach [F. Hariri and M. Ottaviani, Comput.Phys.Commun. 184:2419, (2013); A. Stegmeir et al., Comput.Phys.Commun. 198:139, (2016)], which allows to study realistic diverted geometries with X-point(s) and general boundary contours. We characterise results from turbulence simulations and investigate the effect of geometry by comparing simulations in circular geometry with toroidal limiter against realistic diverted geometry at otherwise comparable parameters. Turbulence is found to be intermittent with relative fluctuation levels of up to 40% showing that a global description is indeed important. At the same time via direct comparison, we find that the Boussinesq approximation has only a small quantitative impact in a turbulent environment. In comparison to circular geometry the fluctuations are reduced in diverted geometry, which is related to a different zonal flow structure. Moreover, the fluctuation level has a more complex spatial distribution in diverted geometry. Due to local magnetic shear, which differs fundamentally in circular and diverted geometry, turbulent structures become strongly distorted in the perpendicular direction and are eventually damped away towards the X-point