Validation of a newly developed FTIR in situ reactor: Real time study of photocatalytic degradation of nitric oxide

For many years, photocatalysis has been proposed as one of the promising techniques to abate environmental pollutants. To improve these reactions it is vital to know the reaction mechanisms of the photocatalytic degradation. This new reactor will make it possible to study the catalytic surface at the moment the reactions occur. By the means of UV LED illumination there is no need of an external UV lamp and thus lowers the cost. The validation of this newly developed reactor is done by investigating the photocatalytic reaction mechanism of nitric oxide (NO) and comparing these findings with those already discussed in literature. From these results, it became clear that the newly developed FTIR in situ reactor allows real time study of photocatalytic degradations.     

The photolysis of ortho-nitrophenols: a new gas phase source of HONO

Formation of nitrous acid (HONO) in the gas phase has been observed for the first time in a flow tube photoreactor upon irradiation (lambda = 300-500 nm) of 2-nitrophenol and methyl substituted derivatives using a selective and sensitive instrument (LOPAP) for the detection of HONO. Formation of HONO by heterogeneous NO2 photochemistry has been excluded, since production of NO2 under the experimental conditions is negligible. Variation of the surface to volume ratio and the nitrophenol concentration showed that the photolysis occurred in the gas phase indicating that HONO formation is initiated by intramolecular hydrogen transfer from the phenolic OH group to the nitro group. From the measured linear dependence of the HONO formation rate on the reactant's concentration and photolysis light intensity, a non-negligible new HONO source is proposed for the urban atmosphere during the day. Unexpectedly high HONO mixing ratios have been observed recently in several field campaigns during the day. It is proposed that the photolysis of aromatic compounds containing the ortho-nitrophenol entity could help to explain, at least in part, this high contribution of HONO to the oxidation capacity of the urban atmosphere.     

Non‐Innocent Methylene Linker in Bridged Lewis Pair Initiators

Deprotonation usually occurs as an unwanted side reaction in the Lewis pair polymerization of Michael acceptors, for which the conjugated addition of the Lewis base to the acid‐activated monomer is the commonly accepted initiation mechanism. This has also been reported for B?P‐based bridged Lewis pairs (BLPs) that form macrocyclic addition products. We now show that the formerly unwanted deprotonation is the likely initiation pathway in the case of Al?P‐based BLPs. In a detailed study of a series of Al?P‐based BLPs, using a combination of single‐crystal diffraction experiments (X‐ray and neutron) and mechanistic investigations (experimental and computational), an active role of the methylene bridge was revealed, acting as a base towards the α‐acidic monomers. Additionally, the polymerization studies proved a living behavior combined with significantly high activities, narrow molecular mass distributions, and the possibility of copolymerization.     

Positron diffusion in metals

Calculations are presented of the positron diffusion constant, mobility and other diffusion related quantities in simple metals. The mobility is found to be largely limited by the positron-phonon interaction which is treated in the deformation potential model. The effect of positron conduction electron scattering is also evaluated and found to be small. The effect of positron impurity scattering is discussed and detailed estimates given for Li in Al. In dilute alloys at moderate temperatures the positron phonon interaction will dominate also over this effect.     

Charge density and experimental electrostatic potentials of two penicillin derivatives

Two penicillin derivatives, the active penamecillin and the inactive penamecillin-1beta-sulfoxide, were used to study the relationship between their charge density and their activity. Single crystals of both compounds were measured at the synchrotron beamline F1 at the HASYLAB/DESY, at 100 K and up to resolutions of around 0.4 A. Experimental charge densities were obtained by using the Hansen-Coppens multipole formalism. The cleavage of the amide bond in the beta-lactam ring is of paramount importance in the mechanism of action of penicillins. Topological analysis of this bond in terms of Bader's AIM theory showed that its strength is equal in both compounds; therefore a direct influence of bond strength on the activity can be ruled out. However, the two derivatives differ significantly in their experimental electrostatic potentials. These differences are discussed and provide further insight into the chemistry and activity of penicillins.     

Fine structure of hearing threshold and loudness perception

Hearing thresholds measured with high-frequency resolution show a quasiperiodic change in level called threshold fine structure (or microstructure). The effect of this fine structure on loudness perception over a range of stimulus levels was investigated in 12 subjects. Three different approaches were used. Individual hearing thresholds and equal loudness contours were measured in eight subjects using loudness-matching paradigms. In addition, the loudness growth of sinusoids was observed at frequencies associated with individual minima or maxima in the hearing threshold from five subjects using a loudness-matching paradigm. At low levels, loudness growth depended on the position of the test- or reference-tone frequency within the threshold fine structure. The slope of loudness growth differs by 0.2 dB/dB when an identical test tone is compared with two different reference tones, i.e., a difference in loudness growth of 2 dB per 10-dB change in stimulus. Finally, loudness growth was measured for the same five subjects using categorical loudness scaling as a direct-scaling technique with no reference tone instead of the loudness-matching procedures. Overall, an influence of hearing-threshold fine structure on loudness perception of sinusoids was observable for stimulus levels up to 40 dB SPL--independent of the procedure used. Possible implications of fine structure for loudness measurements and other psychoacoustic experiments, such as different compression within threshold minima and maxima, are discussed.     

Direct observation of the non-supported metal nanoparticle electron density of states by X-ray photoelectron spectroscopy

Synchrotron-based X-ray photoelectron spectroscopy on copper and silver cluster beams created by a magnetron-based gas-aggregation source has allowed mapping the electron density of states (DOS) of free metallic nanoparticles. The cluster DOS profiles obtained in the experiments strongly resemble the infinite solid DOS shapes, but the extracted cluster work-functions are lower than those for the bulk metal. The latter observation is explained by the initial negative charge on most of the clusters, created by the source.     

Uber die Einwirkung von Licht auf einige feste Salze vom Typus trans-[Co(en)2(NO2)(X)]Y

The influence of sunlight and particularly artificial light with wavelengths λ ≥ 430 nm on two groups of solid complex nitrocobalt(III) salts is investigated: (1) trans-isothiocyanatonitro-bis(ethylendiamine)cobalt(III)-perchlorate, -nitrate and -thiocyanate and (2) trans-chloronitro- and trans-nitratonitro-bis(ethylenediamine)cobalt(III)-nitrate. When the perchlorate of the first group is exposed to sunlight, its colour changes from yellow to red. This change is caused by a partial isomerization of the salt into the corresponding nitrito compound. Under the influence of artificial light with λ ≥ 430 nm the perchlorate and the nitrate of the first group change their colours in the way mentioned. The degree of isomerization under the same experimental conditions is 35 and 47% respectively. Neither the thiocyanate of the first group nor the chloronitronitrate of the second are influenced by the artificial light or sunlight. The absorbance curve of the irradiated nitratonitronitrate in aqueous solution is quite different from that of the non-irradiated. The corresponding nitratonitritonitrate has not been synthesized yet.