Structures of methyl halide dimers in supersonic jets by matrix-isolation infrared spectroscopy and quantum chemical calculations

The CH₃Cl and CH₃Br dimers produced by supersonic-jet expansion were directly deposited on a cold plate using a standard matrix-isolation technique. Dependence of the relative intensities of the observed infrared bands on the stagnation pressure was used to assign the dimer bands appearing near the monomer bands. By a comparison of the wavenumber shifts from the monomer bands with the corresponding values obtained by quantum chemical calculations, DFT/B3LYP/6-311++G(3pd,3df) and MP2/LanL2DZ+fdp, the structures of CH₃Cl and CH₃Br dimers were determined to be a head-to-tail isomer, which is common to the CH₃F and CH₃I dimers determined previously by the same method. The remaining dimer bands, which could not be assigned to the head-to-tail isomer, were tentatively assigned to a head-to-head isomer in analogy with CH₃I dimer.     

Spectrophotometric determination of nitrite produced by flow-electrolysis of nitrate

Summary The electrocatalytic reduction of nitrate to nitrite with a carbon column electrode in the presence of Cu²⁺ and Cd²⁺ was investigated in a flow system. Electrogenerated nitrite was mixed with colour-producing reagents and detected colorimetrically. In acetate and phosphate buffer solutions, the reduction of nitrate to nitrite or further reduction of nitrite was monitored by scanning the electrode potential. In phosphate buffer solution, the yield of nitrite went up to a maximum in the presence of Cu²⁺ and Cd²⁺ at about –1.1V. The electrocatalytic reduction method was applied to the determination of nitrate in river water instead of the conventional Cu-coated Cd column.

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Spektralphotometrische Bestimmung von Nitrit, das durch Durchfluß-Elektrolyse von Nitrat erzeugt wurde

Zusammenfassung Die elektrokatalytische Reduktion von Nitrat zu Nitrit mit Hilfe einer Kohlenstoff-Säulenelektrode in Gegenwart von Cu²⁺ und Cd²⁺ wurde in einem Durchflußsystem untersucht. Das erzeugte Nitrit wurde mit Farbreagentien versetzt und colorimetrisch bestimmt. In Acetat- und Phosphatpufferlösungen wurde die Reduktion von Nitrat zu Nitrit sowie dessen weitere Reduktion mit Hilfe des Elektrodenpotentials verfolgt. Bei –1,1 V in Phosphatpuffer erreicht die Ausbeute an Nitrit in Gegenwart von Cu²⁺ und Cd²⁺ ein Maximum. Die elektrokatalytische Reduktionsmethode wurde an Stelle des konventionellen Verfahrens mit einer Cd-Säule mit Cu-Überzug zur Nitratbestimmung in Flußwasser angewendet.

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This research was supported by Grant-in-Aid for Scientific Research No. 57740288 from the Ministry of Education, Science and Culture of Japan.     

Induced antiferroelectric smectic- C(*)(A) phase by doping ferroelectric- C* phase with bent-shaped molecules

Doping of the ferroelectric Sm-C(*) phase with bent-shaped molecules induces the antiferroelectric Sm-C(*)(A) phase. The effect was observed by means of electro-optic and dielectric measurements in systems with weak interlayer interactions in which the relative strength of anticlinic-synclinic order between molecules in adjacent layers is easily controlled by external factors. Fourier-transform infrared spectroscopy studies suggest that the bent-shaped molecules are not flat. They reorient upon the electric field-induced antiferroelectric-ferroelectric transition to adopt a position in which the average direction of the carbonyl groups is in the smectic plane and a bending tip along the C2 symmetry axis.     

Effect of pulse width and fluence of femtosecond laser on the size of nanobump array

Conical nanobump arrays were generated on gold thin film processed by interfering femtosecond laser. The transition of the height and diameter as functions of fluence and pulse width was investigated. When the fluence was 87 mJ/cm², the height and diameter were not so different at 350 fs or shorter pulse width. They decreased at longer pulse width, and no bump could be generated over 1.6 ps. The results suggest the decrease of size is due to the diffusion of electron to not-excited region, and due to heat conduction to not heated region or substrate, or change of absorbance of laser. At long pulse width of 2.4 ps and relatively higher fluence of 190 mJ/cm², nanobump had liquid-like structure as a stop motion of a water drop.     

Influence of drawing temperature on the strength of fluoride glass fibers

The tensile strength of fluorozirconate glass fibers was measured as a function of fiber drawing temperature, and strengths ranging from 60–220 MPa were observed. Statistical analysis of the strength data points to a bimodal behavior in the fibers drawn at high temperatures, while the mode of fracture is essentially unimodal for fibers drawn at lower temperatures. SEM examination of the fibers drawn at high temperatures revealed the presence of crystals in the fibers, and these crystals were associated with flaws which gave rise to the observed low strength distribution.     

Characteristic features in the collision of chemical waves depending on the aspect ratio of a rectangular field

The photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated on a double rectangular field composed of two rectangular routes, which was drawn using computer software and then projected using a liquid-crystal projector on a filter paper soaked with BZ solution. When two chemical waves were generated on the rectangular routes as the initial condition, the nature of the collision of the waves could be theoretically classified into four categories depending on the initial phase difference between the two waves and the aspect ratio of the rectangular routes. The experimental results were consistent with the features of the theoretical prediction. These results suggest that the feature of wave propagation characteristically develops depending on the geometry of the excitable fields.     

Photoexcited chemical wave in the ruthenium-catalyzed Belousov-Zhabotinsky reaction

The excitation of the photosensitive Belousov-Zhabotinsky (BZ) reaction induced by light stimulation was systematically investigated. A stepwise increase in the light intensity induced the excitation, whereas a stepwise decrease did not induce the excitation. The threshold values for the excitation were found to be a function of the initial and final light intensities, time variation in light intensity, and the concentration of NaBrO(3). The experimental results were qualitatively reproduced by a theoretical calculation based on a three-variable Oregonator model modified for the photosensitive BZ reaction. These results suggest that although the steady light irradiation is known to inhibit oscillation and chemical waves in the BZ system under almost all conditions, the stepwise increase in the light irradiation leads to the rapid production of an activator, resulting in the photoexcitation.     

Surface-enhanced infrared absorption spectroscopic studies of adsorbed nitrate, nitric oxide, and related compounds 1: Reduction of adsorbed NO on a platinum electrode

Surface-enhanced infrared absorption spectroscopy (SEIRA) was used to examine the adsorption state of nitrogen monoxide (nitric oxide, NO) and the reduction of the adsorbed species. The SEIRA spectra gave two distinct bands at 1723-1733 and 1575-1607 cm-1 with an additional weak band at 1656-1676 cm-1 at 0.20 V, the frequencies of which are slightly dependent on the surface coverage. The former two bands are attributed to the on-top and bridged NO, respectively. While the on-top NO stably remained on the surface in the potential range of 0.05 -0.60 V, the bridged NO decreased in its intensity with increasing electrode potential. The reduction of the adsorbed NO obeys first-order kinetics with respect to the adsorbed NO. The rate constants are 2.24 +/- 0.03 and 0.24 +/- 0.09 s-1 at -0.10 V for the on-top and bridged NO, respectively. Tafel slopes obtained from the potential dependence of the rate constant indicate that the rate-determining step is the first electron-transfer process.     

Die optischen Aufheller Fraxin und Aesculin

The closely related glycosides fraxin and esculin have been isolated in pure form from an ash bark extract by gel permeation chromatography. This challenging separation is a prime example for the preparative value of a crosslinked dextran gel. Silicagel 60 only leads to pure esculin. The terms optical brighteners and fluorescence are discussed. All analytical spectra were recorded and are reproduced and interpreted either in the main part or in the supporting information. The project is a follow up of the recent book “Classics in Spectroscopy” by S. Berger und D. Sicker (Wiley‐VCH 2009).