Electronic relaxation time in silver chalcogenides

The electronic relaxation time in silver chalcogenides - typical ionic-electronic conductors - is investigated using a continuum model. The contributions of longitudinal collective modes to the inverse relaxation time are calculated. It is found that in these materials the aperiodic modes, the diffusion mode and the over-damped acoustic phonon modes, play the major role in the electronic scattering processes and the effects of the periodic modes, the damped acoustic and optical phonon modes, are trivial, in contrast to the cases in ordinary polar crystalline solids.     

Resonant two photon spectrum in a Doppler broadened line

The line shape in the resonant and near resonant two photon absorption spectra in the $\text{Na 3S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?3P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{?5S}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ transition was investigated using two single frequency dye lasers. Two types of Doppler-free peaks for resonant case and Doppler-broadened normal two photon peaks were observed. They were different in the width, selection rule and the laser power dependence in agreement with theory.     

Photoisomerization of 1,2-diphenylcyclopropane sensitized by polypeptides containing naphthalene groups in their side chain

Poly(γ-1-naphthylmethyl L - and DL -glutamate) (PNLG and PNDLG) and copolypeptides of γ-1-naphthylmethyl L -glutamate and γ-benzyl-L -glutamate were used as sensitizers for isomerization of trans-1,2-diphenylcyclopropane. Quantum yields relative to that of 1-methylnaphthalene were measured in dichloroethane (DCE) and dichloroacetic acid (DCA). The relative quantum yield in DCE was smaller than unity for PNLG, but greater than unity for PNDLG and copolypeptides. The result is discussed in terms of increased effective collisional radius and energy trapping by excimer formation. The relative quantum yields in DCA were close to unity except for the copolypeptides of higher γ-benzyl L -glutamate content. This suggests that the naphthalene groups act in the same manner as their monomeric counterparts in the random conformation and that the greater proportion of γ-benzyl L -glutamate in the copolypeptides lowers the quantum efficiency because trans-1,2-diphenylcyclopropane must penetrate through the polymeric medium in order to encounter the excited naphthalene.     

Frequency dependence of the spin-lattice relaxation time in solid H2 with very low concentration of ortho-molecules

By extending the previous theory of Hama et al. for the spectral density in the system of randomly distributed spins with R^–n-interactions, the frequency dependence of the spin-lattice relaxation time of o-H₂ in solid H₂ at very low concentration is studied, with results in excellent agreement with measurements. In the present extension the effects of the anisotropy and rotational Zeeman energies have been taken into account by the use of the measured constants relevant to both energies.     

Carbon-13 nuclear magnetic resonance spectra of some methyl and phenyl substituted 2H-azirines

Carbon-13 n.m.r. spectra have been obtained for some methyl and phenyl substituted 2H-azirines. The higher field resonance of C-2 than that of the corresponding aziridine carbon is interpreted in terms of ring strain. Substituent effects on the chemical shifts of the azirine ring carbons are discussed. A set of additivity parameters for the methyl and phenyl groups are obtained which can be used for the calculation of the chemical shifts of the azirine ring carbons. The substituent effect of an azirine ring on the chemical shift of benzene is also discussed in comparison with those of some other substituents. A high degree of s character (48.5%) in the exocyclic orbital of C-3 is indicated by a large J(¹³C-3,H) value (242.5 Hz).     

Synthesis and polymerization of heteroaromatic vinyl monomers

Methods of preparing new monomers, 2-vinyl and 2-isopropenyloxazoles and 2-isopropenyl-1,3,4-oxadiazoles are described. New methods were developed to synthesize monomers containing an isoxazole or a thiazole ring. Radical homopolymerization and copolymerization with styrene of these monomers were carried out by using AIBN as an initiator. Monomer reactivity ratios r₁, r₂ and Alfrey-Price Q–e values were determined by the Fineman-Ross and the Mayo-Lewis methods. The localization energy of the β-carbon was calculated by a HITAC-5020 computer, and the monomer reactivity is discussed in terms of L_β.     

The β‐silicon effect. 4: substituent effects on the solvolysis of 1‐alkyl‐2‐(aryldimethylsilyl)ethyl trifluoroacetates

Solvolysis rates of 2‐(aryldimethylsilyl)‐1‐methylethyl and 2‐(aryldimethylsilyl)‐1‐tert‐butylethyl trifluoroacetates were determined conductimetrically in 60% (v/v) aqueous ethanol. The effects of aryl substituents at the silicon atom on the solvolysis rates at 50 °C were correlated with parameters of r⁺ = 0.15 with the Yukawa–Tsuno equation, giving ρ values of ?1.5 for both secondary α‐Me and α‐tert‐Bu systems. The ρ values for those secondary systems are less negative than ?1.75 for the 2‐(aryldimethylsilyl)ethyl system that proceeds by the Eaborn (non‐vertical) mechanism, while they are distinctly more negative than ?0.99 for 2‐(aryldimethylsilyl)‐1‐phenylethyl system that should proceed by the Lambert (vertical) mechanism. There was a fairly linear relationship between the reaction constants (ρ) for the β‐silyl substituent effects and the solvolysis reactivities for a series of β‐silyl substrates. The solvolyses of the α‐Me and tert‐Bu substrates proceed through the transition state (TS) with an appreciable degree of the β‐silyl participation, close to the Eaborn (non‐vertical) TS rather than to the Lambert (vertical) TS. Copyright © 2010 John Wiley & Sons, Ltd.