Comment on “optical homogeneous linewidths of resorufin in ethanol glass: an apparent contradiction between hole-burning and photon-echo results?”

Inaccurate speculations (Chem. Phys. Letters 137 (1987) 201) that photon-echo measurements on resorufin in ethanol glass (Chem. Phys. Letters 120 (1986) 6; J. Chem. Phys. 86 (1987) 77) were performed on the glassy plastic crystal phase of ethanol and were systematically in error are corrected. Control experiments reported in the original papers and recent results on resorufin in glycerol, which does not form multiple phases, are cited. The original conclusion that photon-echo and hole-burning experiments measure different physical properties in these systems is confirmed. Recent theoretical work has shown that the difference between the two experiments results from slow relaxation processes known to exist in glasses and that the comparison of the two experiments is a valuable means of studying these processes.     

Correlation between glass transition and crystallization phenomena in context of Meyer–Neldel rule

The physical origin of the glass transition and its possible connection with crystallization is still an unresolved problem of glass science. Recent publications demonstrate the strong evidence of intrinsic relation between glass transition and crystallization phenomena. Here, we study this problem by using Meyer–Neldel rule (MNR) as a tool. The observation of MNR in thermally activated non-isothermal crystallization was verified by us in past. The objective of the present work is to check the applicability of MNR for thermally activated non-isothermal glass transition and crystallization in some chalcogenide glasses. We found that like crystallization, the glass transition phenomenon also obeys the MNR.     

Catalyst deactivation kinetics: An apparent delay in decreasing of catalyst activity, “inflection point” and data interpretation

Problems of catalyst deactivation kinetics and catalyst stability testing are considered. An apparent delay of deactivation and its interpretation is discussed. The coordinates of inflection points on the curves of conversion decay are also considered. The influence of reaction and deactivation kinetics, as well as type of laboratory reactor on inflection point is analysed. Several helpful and practical equations, as well as real examples are presented.     

Polarized Light and Quantum Mechanics: An Optical Analog of the Stern–Gerlach Experiment

Lecture demonstrations involving polarization of light are presented and discussed from the quantum theoretical point of view. The demonstrations clearly show that only two base states are required to describe the quantum state of a photon and they illustrate an optical analog of the Stern—Gerlach experiment that involved electrons.     

Dephasing time in solids and homogeneous optical linewidth: are the mechanisms of the electron-phonon coupling the same?

The differences between theoretical formulas for the reciprocal dephasing time T₂⁻¹ and the homogeneous optical linewidth γ are discussed. Both are due to the same mechanism (quadratic electron-phonon coupling), but it is treated more approximately in the formula for T₂⁻¹.     

An interesting competition between 6π-electro- and Garratt–Braverman cyclization in bis-diene-allene sulfones: synergy between experiment and theory

The reactivity of a series of bispropargyl sulfones with an ortho alkenyl moiety was studied. Under basic condition, these molecules isomerized to the bis-diene-allene system capable of undergoing 6π-electro-(EC) as well as Garratt–Braverman (GB) cyclization. The reaction generally favours the GB process but the balance can be tilted towards the 6π-EC pathway by suitable perturbation of structure and temperature. The findings are useful as the systems undergoing GB pathway can show DNA-damage activities.     

Conformer assignment of OH stretches in ethanol and isopropanol

Rigid harmonic asymetric top contour simulation is applied to assign the OH stretch transitions observed in the vapour phase infrared spectra of ethanol and isopropanol to gauche and trans conformers. For hetanol, the high frequency ν(OH) absorption must be assigned to the trans, for isopropanol the high frequency absorption is found to be due to the gauche conformer.     

An ESR and Optical Spectroscopic Study of the Mechanism of Photostimulated Reactions in Hydrogen Cyanide γ-Irradiated at 77 K

Changes in the electronic absorption spectra and ESR spectra in the course of photobleaching of radiolyzed solid HCN with light of different wavelengths (236–600 nm) were studied by ESR and optical spectroscopy. Two bands at 270 and 290 nm in the optical spectrum were attributed to the presence of H₂C=N and HC=NH radicals, respectively (the molar absorption coefficients are k ₂₇₀ 2.7 × 10²l mol^–1cm^–1and k ₂₉₀ 1.5 × 10²l mol^–1cm^–1, respectively). Structureless broad bands with maximums at 313 and 465 nm, which were detected after the exposure of a sample to light with 300 nm, can belong to the cyanide ions (CN^–) and H₂C=N⁺cations (the molar absorption coefficients of the ions are k _ion= (0.4–1.0) × 10²l mol^–1cm^–1). In the photobleaching of -irradiated HCN ( = 236–280 nm), H₂C=N⁺radicals were additionally formed by the photoinduced reaction of electron transfer from the CN^–anion to the H₂C=N⁺cation. The amount of these radicals generated in the course of photobleaching is several times greater than that of the same radicals formed in the radiolysis via hydrogen atom addition to the multiple bond of HCN molecules.     

Kinetics and nucleation mechanism of carbamazepine–saccharin co-crystals in ethanol solution

Journal of Thermal Analysis and Calorimetry - This study aimed to investigate the metastable zone width (MSZW) and the nucleation order of carbamazepine–saccharin (CBZ–SAC) co-crystals...     

Enthalpy recovery in polymeric glasses: Does a correlation exist between the empirical (T-N-M) relationship parameters and the glass structures?

To characterize the enthalpy recovery which appears during physical aging in glassy materials and especially in glassy polymers, the empirical Tool-Narayanaswamy-Moynihan (TNM) relationship for the relaxation time is widely used. This relationship depends essentially on three parameters, the apparent activation energy Δh*, the non linearity parameter x and the fictive temperature T_f. Even if a great amount of data (x, Δ*) can be found in the literature, no direct correlation between the values of these parameters and the engaged structures are available. On the one hand, using some polymers like Poly(ethylene terephthalate), Polymethyl(α-n-alkyl)acrylates and three dimensional epoxy networks for which structural changes are controlled and on the other hand, using some recently published results concerning other materials including inorganic polymers (Ge-Se and Ge-Te glasses), we show that it is possible to propose some interesting tendencies. In particular it is shown that the value of x depends on the intermolecular strength for organic polymers and on the connectivity for inorganic polymer.     

Comparability of measurement results for pesticide residues in foodstuffs: an open issue?

The dispersion of results from proficiency tests for the analysis of pesticide residues in foodstuffs suggests that improvements in the compatibility of measurement results are needed. Currently observed divergences can make the evaluation conclusion on foodstuffs compliance with certain legislation dependent on the consulted laboratory. This work discusses the origin and impact of this lack of compatibility, following the metrological concepts presented at the latest version of the “International Vocabulary of Metrology” (VIM3), thus allowing for a clear diagnostic of the problem. The reporting of results from different measurement methods uncorrected for the observed analyte recovery makes them traceable to different “operationally defined measurement procedures” (VIM3) and, therefore, not comparable. When results from different measurement methods are reported corrected for analyte recovery, R, and R is different for spiked and incurred residues, measurement results may be not compatible if this effect is not considered on the uncertainty budget. This discussion is illustrated with metrological models for any possible combination of “measurement performance” and “maximum residue level”. These models are complemented with experimental data of the analysis of pesticide residues in a sample of ginseng powder from a proficiency test. The adopted experimental design allowed the identification of additional threats to metrological compatibility in this field. Solutions to the faced problem are discussed for practicability and impact on regulatory issues. The use of a universal “reference measurement procedure” proves to be the most feasible way of ensuring comparability of measurements in this field.     

Kinetic study of the mass transfer of S-Tr?ger's base in the system cellulose triacetate and ethanol.

A recent study of the mass transfer kinetics of (-)- or S-Tr?ger's base (TB) between ethanol and microcrystalline cellulose triacetate (CTA) allows an analysis of the concentration dependence of the mass transfer rate coefficient (k(m)). S-TB elutes before R-TB. The retention time of the both compounds decreases with increasing temperature. In this study, experimental data measured between 30 and 50 degrees C were analyzed to provide information on the kinetics of several mass transfer processes which take place in the chromatographic column, i.e., axial and intraparticle dispersion, the fluid-to-particle mass transfer, and the kinetics of adsorption/desorption at the actual adsorption sites. Intraparticle diffusion has the dominant contribution to band broadening at high flow-rates. Both intraparticle diffusivity and the surface diffusion coefficient exhibit a small concentration dependence. The positive dependence of k(m) on the concentration of S-TB seems to result from the properties of the adsorption/desorption kinetics and can be interpreted by considering the phase equilibrium properties. A quantitative analysis of the activation energy of the mass transfer kinetics of S-TB in the CTA column was also attempted.     

Competition between receptors in dynamic combinatorial libraries: amplification of the fittest?

Dynamic combinatorial chemistry is a powerful tool for the discovery of strong binders (synthetic receptors or ligands) because binding causes a shift in the equilibrium of library members toward those that bind well. Ideally, the best binders are selectively amplified. However, theoretical studies predict this is not always the case. This paper describes the first quantitative experimental evidence proving that, under special circumstances, the preferential amplification of suboptimal synthetic receptors can indeed occur. Our results also demonstrate that reducing the amount of guest in the library can rectify such undesirable behavior and ensures selective amplification of the fittest receptor.     

Nanoscale imaging of hydrogen and sodium in alteration layers of corroded glass using ToF-SIMS: Is an auxiliary sputtering ion beam necessary?

The hydrogen (H)/sodium (Na) interface is of great interest in glass corrosion research. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is one of the few techniques that can provide nanoscale H and Na imaging simultaneously. However, the optimized condition for ToF-SIMS imaging of H in glass is still unclear. In H depth profiling using ToF-SIMS, H background control is a key, in which an analysis ion beam and a sputtering ion beam work together in an interlaced mode to minimize it. Therefore, it is of great interest to determine if an auxiliary sputtering ion beam is also necessary to control H background in ToF-SIMS imaging of H. In this study, H imaging with and without auxiliary sputtering beams (Cs⁺, O₂⁺, and Ar_n⁺) was compared on a corroded international simple glass (ISG). It was surprising that the H/Na interface could be directly imaged using positive ion imaging without any auxiliary sputtering ion beam under a vacuum of 2 to 3 × 10⁻⁸ mbar. The H⁺ background was about 5% atomic percent on the pristine ISG glass, which was significantly lower than the H concentration in the alteration layer (~15%). Moreover, positive ion imaging could show distributions of other interesting species simultaneously, providing more comprehensive information of the glass corrosion. If an auxiliary O₂⁺ sputtering ion beam was used, the H⁺ background could be reduced but still higher than that in the depth profiling. Besides, this condition could cause significant loss of signal intensities due to strong surface charging.     

How to calculate uncertainties of neutron flux parameters and uncertainties of analysis results in k0-NAA?

A novel method is presented for the calculation of uncertainties of neutron flux parameters and element mass fractions and their uncertainties in k₀-neutron activation analysis (k₀-NAA) using the Kragten universally applicable spreadsheet technique. The results obtained are compared with other approaches for evaluation of uncertainties of the neutron flux parameters and element mass fractions, namely with the Kayzero for Windows, k0-IAEA and ERON programs. The differences observed are discussed in terms of how the above programs take into account various uncertainty sources and their correlations.