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[en] The hunt for complex organic molecules (COMs) is a major concern for understanding the possible role of interstellar chemistry in the synthesis of the molecules that ultimately may be at the origin of life. A comprehensive screening of the 14 species effectively observed under 32 different isomeric forms in the interstellar medium has been done by means of high-level quantum chemical simulations. Confrontation between calculations and observations shows that when several isomers of the same generic formula are identified, it is always the most stable one that is the most abundant. Moreover, the abundance ratio of the most stable isomer to the other isomers is directly related to their energy difference. What can be seen as a minimum energy principle is verified in molecular clouds, hot cores/corinos, photodissociation regions, and asymptotic giant branch stars. The few exceptions encountered could be rationalized either by the existence of different routes of formation with no intermediate in common and/or specific depletion on the grains of one isomer with respect to the others.
[en] CH_2Cl–Cl and CH_2Br–Br, photoisomers of CH_2Cl_2 and CH_2Br_2 , were identified in the matrix IR spectra from the precursors exposed to plume radiation of a laser-ablated transition metal. On the other hand, the corresponding photoisomers of CH_2F_2 and CH_2FCl (CH_2F–F, CH_2F–Cl, and CH_2Cl–F) were not observed because of their instabilities. The C[BOND]X bond of the product is unusually strong, leading to a high C[BOND]X stretching frequency. Natural bond orbital (NBO) analysis reveals that it is a true carbon–halogen double bond; in contrast, the X[BOND]X bond is largely ionic (H_2C[DOUBLE BOND]X"δ"+ ∙∙∙X"δ"− ), similar to the previously studied analogs from tri- and tetrahalomethanes. Intrinsic reaction coordinate (IRC) computation reproduces the smooth interconversion between the precursor and the energetically higher photoisomer, consistent with the disappearance of the product during visible photolysis
[en] Light induced electron transfer of metal complexes has been studied extensively during the last decade. This interest was stimulated by attempts to develop an artificial photosynthesis for the conversion and chemical storage of solar energy. Even if this goal has not yet been achieved photochemical redox processes of coordination compounds are now much better understood. In this review the various possibilities of photoinduced electron transfer are discussed and illustrated by selected samples. A distinction is made between intra- and intermolecular electron transfer which may occur as a direct optical transition or by an excited state electron transfer mechanism. (author). 52 refs.; 1 fig
[en] Full text:It is known, that the photosynthetic apparatus of plants differs with high sensitivity to action of lines stress factor (for example, high and low temperatures, lack of water or flooding, sanotiazol, pesticides, heavy metals and radionuclides, various pollutants of air) including to action of electromagnetic fields (EMF) practically all sites of a spectrum of radio frequencies. Proceeding from above-stated studying of behaviour of a photo synthesizing cell functioning under action photosynthetic active radiation is interesting at simultaneous action of electromagnetic radiation of high frequency
[en] Pety et al. have reported the detection of eight transitions of a closed-shell, linear molecule (B11244) in observations toward the Horsehead photodissociation region (PDR), which they attribute to the l-C3H+ cation. Recent high-level ab initio calculations have called this assignment into question; the anionic C3H– molecule has been suggested as a more likely candidate. Here, we examine observations of the Horsehead PDR, Sgr B2(N), TMC-1, and IRC+10216 in the context of both l-C3H+ and C3H–. We find no observational evidence of Ka = 1 lines, which should be present were the carrier indeed C3H–. Additionally, we find a strong anticorrelation between the presence of known molecular anions and B11244 in these regions. Finally, we discuss the formation and destruction chemistry of C3H– in the context of the physical conditions in the regions. Based on these results, we conclude there is little evidence to support the claim that the carrier is C3H–.
[en] We report improvements in the detection limit and responsivity of biomimetic hair-flow sensors by electrostatic spring softening. Applying a dc-bias voltage to our capacitive flow sensors results in a reduced sensory threshold, improving the mechanical transfer and flow detection limit by more than 6 dB. We further show that the sensor's responsivity for airflows is also improved on application of high-frequency ac-bias voltages to the sensor's capacitive structures with little sensitivity to the bias frequency. (paper)
[en] Graphical abstract: A recent classical description of photodissociation dynamics in a quantum spirit is applied for the first time to a realistic process, the fragmentation of NeBr2. Highlights: ► The photo-dissociation of NeBr2 is studied by means of two approaches. ► The first is the standard classical one with Gaussian binning. ► The second is a new method applied for the first time to a realistic system. ► The new method leads to exactly the same results as the standard one. ► However, it requires about 10 times less trajectories in the present case. - Abstract: The recent classical dynamical approach of photodissociations with Bohr quantization [L. Bonnet, J. Chem. Phys. 133 (2010) 174108] is applied for the first time to a realistic process, the photofragmentation of the van der Waals cluster NeBr2. We illustrate the fact that this approach, formally equivalent to the standard one, may be numerically much more efficient.
[en] Interception of radiation and the consequent potential photosynthesis was studied, by sing a simulation model, in structurally different forest stands at latitudes 40° and 60°. The studied stands were of two different types with respect to the leaf-area distribution: horizontally homogenous canopies and canopies with an aggregation of leaves into individual crowns. The effect of canopy structure on interception of radiation and photosynthesis was studied by varying leaf area index, stand density, and crown size and shape. In none of the studied cases was the relationship between accumulated radiation interception and photosynthesis strictly linear, but on a longer time-scale (one growing season) this non-linearity was not very pronounced. Neither canopy structure nor latitude substantially affected the slope of the relationship. In conclusion, while properties of canopy structure and incoming radiation determine the actual amount of radiation intercepted by the canopy, the conversion efficiency between intercepted radiation and photosynthesis appeared to be rather insensitive to differences in canopy structure and in properties of incoming radiation. (author)