Fits to new calculations of photoionization cross sections for low-Z elements

Analytical approximations to results of new calculations of partial (i.e. by subshell) photoionization cross sections of elements (2 < Z < 30, Z = 36) are presented which cover the photon energy range from near threshold to 300 keV. The computer program developed by Brysk and Zerby, which is based on the single-electron model and uses screened self-consistent field and Dirac-Slater wave function data furnished by Cromer, Waber and Liberman, was used. Sufficient multipoles were included to calculate the partial cross sections within a few per cent, on the assumed model. Results for several elements are compared with other calculations and measurements of total photoionization cross sections. The results are presented in a form most convenient for calculations of opacities of hot gases.     

Group mean emissivities and opacities of high temperature SiO2

Absorption and extinction coefficients of SiO₂ have been calculated using a mean ion model but with the most important singly and multiply excited states of the dominant ionic species considered explicitly. Free-free, bound-free, bound-bound, and scattering are taken into account. Densities range from 10^-6 to 10³ g cm^-3 and temperatures range from 30 to 10 keV. Emissivities are obtained from detailed balance. Group means are given for some representative cases.     

Oxoselenido clusters of the lanthanides: rational introduction of oxo ligands and near-IR emission from Nd(III)

Reactions of Ln(SePh)3 with SeO2 in THF give octanuclear oxoselenido clusters with the general formula (THF)8Ln8O2Se2(SePh)16 (Ln = Ce, Pr, Nd, Sm). In this isomorphous series, the eight Ln(III) ions are connected in the center by a pair of mu3-O2- ligands and mu5-Se2- ligands, with 14 bridging and two terminal selenolate ligands capping the cluster surface. Thermal decomposition at 700 degrees C of the Nd compound in vacuo led to the formation of a phase mixture of NdSe2, Nd2Se3, and Nd2O3. Near-IR emission experiments on the (THF)8Nd8O2Se2(SePh)16 and the fluorinated thiolate compound (DME)2Nd(SC6F5)3 demonstrate that clusters with oxo ligands are not only highly emissive, but also they emit at wavelengths not found in conventional oxides.     

NMR on gallium single crystals: Not yet an absolute thermometer at very low temperatures

A twin crystal of Ga was investigated in the temperature and field ranges of 0.5 to 10 mK and 60 to 250 mT, respectively. In these fields the magnetic interaction is too large to be treated as a perturbation of the quadrupolar interaction. Therefore, the eigenvalues of the Schrödinger equation were calculated numerically, and then used to determine the crystalline axes by pulsed NMR on ⁶⁹Ga and ⁷¹Ga. The temperature dependence of the NMR line intensities was measured using ¹⁹⁵Pt-NMR for thermometry. The observed intensities do not follow the theoretical expectations for a spin system of low nuclear polarization. In addition, a temperature-dependent frequency shift was observed. These results suggest that the effect of interactions between the spins, as well as more complicated spin dynamics, need to be considered in order to use gallium as an absolute thermometer at temperatures below 1 mK.     

APPARATUS FOR RECORDING LIGHT FLASH INDUCED MEMBRANE VOLTAGE TRANSIENTS WITH 10 ns RESOLUTION

Abstract— Apparatus for recording voltage waveforms resulting from flash illumination of bilayer membranes with sorbed dyes or pigments are described. Time constants of light-induced molecular events which displace electric charge in membranes can be taken directly from these waveforms. The waveforms induced across bilayer membranes by a carbocyanine dye and by chlorophyllin illustrate the apparatus performance. The risetime of the chlorophyllin induced photo-voltages are ˜10ns.     

PHOTOELECTRIC EFFECTS FROM CHLOROPHYLL a IN BILAYER MEMBRANES

Abstract— The photophysical and photochemical properties of thiophene derivatives have been studied by fluorescence and by 353 nm laser flash spectroscopy. α-Terthienyl and its derivatives show a moderate fluorescence quantum yield (less than 0.1) in cyclohexane, ethanol, or TritonX–100 micelles. An additional thiophene ring increases this value to 0.2 in ethanol or micelles. The transient triplet state of the six thiophenes is characterized by strong absorptions (ε⋍ 50000 M ^-1 cm^-1) in the visible region. These triplet states are very long lived. They react with oxygen, producing singlet oxygen very efficiently because of their high quantum yield of triplet formation (0.1 to 0.3). They do not react with excellent hydrogen or electron donors such as indole, N-acetyl tryptophanamide or cysteine. The hydrophobic thiophenes investigated are, therefore, Type II photodynamic agents almost exclusively.