The Pauli Principle and Chemical Bonding in Molecules and Solids

The starting point of this contribution is a discussion of the concept of exchange interactions and its relation to chemical bonding and valence. Then, a class of phenomena characterized by weak chemical bonding (?1eV) in solids and molecules is analyzed in more detail, with “superexchange” in insulating solids with paramagnetic 3d-cations serving as prototype. A model of “effective electrons” is developed for weak bonding on the basis of exchange perturbation theory, taking full account of the Pauli principle. The model is applied to: (i) magnetic interactions in solids (interaction energy 10^?2 to 10^?4 eV); (ii) stability of noble-gas halides (binding energy ≈ 1eV); and (iii) rotational barriers in simple molecules (barrier heights of several 0.1 eV).     

Extreme value estimation for discretely sampled continuous processes

In environmental applications of extreme value statistics, the underlying stochastic process is often modeled either as a max-stable process in continuous time/space or as a process in the domain of attraction of such a max-stable process. In practice, however, the processes are typically only observed at discrete points and one has to resort to interpolation to fill in the gaps. We discuss the influence of such an interpolation on estimators of marginal parameters as well as estimators of the exponent measure. In particular, natural conditions on the fineness of the observational scheme are developed which ensure that asymptotically the interpolated estimators behave in the same way as the estimators which use fully observed continuous processes.     

Correlated,Dual‐Beam Optical Gating in Coupled Organic–Inorganic Nanostructures

An optical switch with two distinct resonances is formed by combining PbS nanocrystals and the conductive polymer poly[sodium 2‐(2‐ethynyl‐4‐methoxyphenoxy)acetate] (PAE) into a hybrid thin film. Infrared excitation of the nanocrystals invokes charge transfer and consecutive polaron formation in the PAE, which activates the switch for excited‐state absorption at visible frequencies. The optical modulation of the photocurrent response of the switch exhibits highly wavelength‐selective ON/OFF ratios. Transient absorption spectroscopy shows that the polaron formation is correlated with the excited state of the nanocrystals, opening up new perspectives for photonic data processing. Such correlated activated absorption can be exploited to enhance the sensitivity for one optical signal by a second light source of different frequency as part of an optical amplifier or a device with AND logic.     

Spectro-Microscopic Techniques for Studying Nanoplastics in the Environment and in Organisms

Nanoplastics (NPs), small (<1 μm) polymer particles formed from bulk plastics, are a potential threat to human health and the environment. Orders of magnitude smaller than microplastics (MPs), they might behave differently due to their larger surface area and small size, which allows them to diffuse through organic barriers. However, detecting NPs in the environment and organic matrices has proven to be difficult, as their chemical nature is similar to these matrices. Furthermore, as their size is smaller than the (spatial) detection limit of common analytical tools, they are hard to find and quantify. We highlight different micro-spectroscopic techniques utilized for NP detection and argue that an analysis procedure should involve both particle imaging and correlative or direct chemical characterization of the same particles or samples. Finally, we highlight methods that can do both simultaneously, but with the downside that large particle numbers and statistics cannot be obtained.     

Visible Light-fueled Mechanical Motions with Dynamic Phosphorescence Induced by Topochemical [2+2] Reactions in Organoboron Crystals

In the quest for essential energy solutions towards an ecological friendly future, the transformation of visible light/solar energy into mechanical motions in metal-free luminescent crystals offers a sustainable choice of smart materials for lightweight actuating, and all-organic electronic devices. Such green energy-triggered photodynamic motions with room temperature phosphorescence (RTP) emission in molecular crystals have not been reported yet. Here, we demonstrate three new stoichiometrically different Lewis acid-base molecular organoboron crystals (PS1, PS2, and PS3), which exhibit rapid photosalient effects (ballistic splitting, moving, and jumping) under both ultraviolet (UV) and visible light associated with quantitative single-crystal-to-single-crystal (SCSC) [2+2] cycloaddition of preorganized olefins. Furthermore, these systems respond to sunlight and mobile (white) flashlight with a complete SCSC transformation in a relatively slow fashion. Remarkably, all PS1, PS2, and PS3 crystals display visible light-promoted dynamic green RTP as their emission peaks promptly blue-shift, due to instantaneous photomechanical effects. Time-dependent structural mapping of intermediate photoproducts during fast SCSC [2+2] photoreaction, by X-ray photodiffraction, reveals a rationale for the origin of these photodynamic motions associated with rapid topochemical transformations. The reported light-driven behavior (mechanical motions, dynamic phosphorescence, and topochemical reactivity), is considered advantageous for the strategic design of stimuli-responsive multi-functional crystalline materials.     

Magnetic trapping and Zeeman relaxation of NH (X3Sigma-)

NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with 3He is measured to be 3.8+/-1.1 x 10(-19) cm(2) at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of gamma=7 x 10(4), in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K?os, and G. Cha?asiński, Phys. Rev. A 68, 051401 (2003)10.1103/PhysRevA.68.051401].     

Reproducibility experiments on measuring acoustical properties of rigid-frame porous media (round-robin tests)

This paper reports the results of reproducibility experiments on the interlaboratory characterization of the acoustical properties of three types of consolidated porous media: granulated porous rubber, reticulated foam, and fiberglass. The measurements are conducted in several independent laboratories in Europe and North America. The studied acoustical characteristics are the surface complex acoustic impedance at normal incidence and plane wave absorption coefficient which are determined using the standard impedance tube method. The paper provides detailed procedures related to sample preparation and installation and it discusses the dispersion in the acoustical material property observed between individual material samples and laboratories. The importance of the boundary conditions, homogeneity of the porous material structure, and stability of the adopted signal processing method are highlighted.