Spin-Orbit coupling in aromatic hydrocarbons: A semiempirical evaluation of the radiative lifetimes of naphtalene and anthracene

Singlet-triplet spin-orbit matrix elements, which govern the lowest ³B_1u ← ¹A_g transition in typical aromatic molecules like naphtalene and anthracene, are calculated with INDO molecular orbitals and the conventional spin-orbit one-electron hamiltonian. The correct order of magnitude of the triplet radiative lifetimes is obtained for the two molecules, when INDO MO coefficients are referred to a symmetrically orthogonalized basis. The possibility of using the semiempirical Hamiltonian is explored using ab initio wave-functions for a few test cases. Reasonably accurate doublet-doublet and singlet-triplet matrix elements have been computed.     

Growth mechanism of octahedron-like BaMoO4 microcrystals processed in microwave-hydrothermal: Experimental observations and computational modeling

Octahedron-like BaMoO4 microcrystals were synthesized by the co-precipitation method at room temperature and processed in microwave-hydrothermal at 413 K for different times （from 30 min to 5 h）. These microcrystals were analyzed by X-ray diffraction （XRD）, field-emission gun scanning electron microscopy （FEG-SEM） and transmission electron microscopy （TEM）. XRD patterns showed that this material presents a tetragonal structure without the presence of deleterious phases. FEG-SEM and TEM micrographs revealed that the BaMoO4 microcrystals present an octahedron-like morphology with agglomerate nature and polydisperse particle size distribution. These micrographs also indicated that the microcrystals grow along the [0 01 ] direction. The observed crystallographic planes in these structures were modeled computationally and a crystal growth model was proposed in order to explain the morphological changes as a function of processing time.     

Fluxional Behaviour of Isocyanide Derivatives of Dodecacarbonyltetrairidium

The fluxional behaviour of [Ir₄(CO)₁₁(t-BuNC)] ( 1 ) and [Ir₄(CO)₁₁(ArNC)] (Ar = 4-methoxyphenyl, 4-tolyl, phenyl, 4-chlorophenyl, 4-nitrophenyl; 2 – 5 ) has been investigated by 2D and variable-temperature ¹³C-NMR. These techniques give new evidence of the processes responsible for CO exchange, namely two successive merry-go-rounds causing Cotton-like scrambling and a CO rotation about one metal center.     

Advection-induced spectrotemporal defects in a free-electron laser

We evidence numerically and experimentally that advection can induce spectrotemporal defects in a system presenting a localized structure. Those defects in the spectrum are associated with the breakings induced by the drift of the localized solution. The results are based on simulations and experiments performed on the super-ACO free-electron laser. However, we show that this instability can be generalized using a real Ginzburg-Landau equation with (i) advection and (ii) a finite-size supercritical region.     

Electronic propensity rule for radiationless transitions

We show theoretically and empirically that non-radiative rate constants tend to vary in accordance with competing radiative rate constants. The analysis is used to compare intersystem crossings and heavy-atlom effects in aromatic hydrocarbons.     

Model for the direct photo-isomerization of stilbene

The photo-chemical cis-trans isomerization of stilbene is re-interpreted after the introduction of a low-energy doubly excited state.     

Laminar flow in a complex geometry: A comparison

This paper reports on the outcome of a workshop of the IAHR Working Group on Refined Modelling of Flows on the subject of computing laminar flows in complex geometries. Flow inside a channel with a smooth expansion was chosen by the organizers of the workshop as a suitable test case for assessing the capabilities of current numerical methods. The results obtained by fifteen participant groups are presented and compared against a suitable benchmark solution. The most important considerations that emerged at the workshop are briefly reported and the conclusions arising from an analysis and comparison of the various solutions are finally provided.