Hyperfine field and diffusion of μ+ in Fe single crystals

In recent positive-muon spin rotation experiment at TRIUMF on single crystal Fe, a clear temperature dependent change has been observed, for the first time, both in frequency and depolarization rates from 300 K down to 23 K. The μ⁺ depolarization was explained by the μ⁺ diffusion through inhomogeneous dipolar fields and the diffusion constant was found to obey an Arrhenius law (activation energy 17 meV) above 70 K but surprisingly deviated from this at lower temperatures, indicating quantum diffusion. We have also found that the μ⁺ hyperfine field has a temperature dependence slightly stronger than that of the magnetization.     

The stereochemistry of attack by a carbon electrophile on a tin-carbon bond

In the cyclisation of the 5-stannyl aldehyde (3), the cyclopentanol ring (4) is formed with retention of configuration at the carbon bearing the stannyl group.     

An adaptation of the lattice gas to the water problem. II. Second-order approximation

The adaptation of the lattice-gas model to embody features possessed by water is further explored. On the basis of Martin's functional derivative formulation of Ising problems, a perturbation scheme is developed which allows calculation of the free energy to any desired order in the interaction potential at fixed density. The free energy correct to second order in the interaction strength is utilized here for calculation of other thermodynamic properties of the model. With reasonable choices of values of the interaction parameters these thermodynamic properties of the model can be brought into agreement with those of real water.     

Recombination dynamics and hydrogen abstraction reactions of chlorine radicals in solution

We observe chlorine radical dynamics in solution following two-photon photolysis of the solvent, dichloromethane. In neat CH(2)Cl(2), one-third of the chlorine radicals undergo diffusive geminate recombination, and the rest abstract a hydrogen atom from the solvent with a bimolecular rate constant of (1.35 +/- 0.06) x 10(7) M(-1) s(-1). Upon addition of hydrogen-containing solutes, the chlorine atom decay becomes faster, reflecting the presence of a new reaction pathway. We study 16 different solutes that include alkanes (pentane, hexane, heptane, and their cyclic analogues), alcohols (methanol, ethanol, 1-propanol, 2-propanol, and 1-butanol), and chlorinated alkanes (cyclohexyl chloride, 1-chlorobutane, 2-chlorobutane, 1,2-dichlorobutane, and 1,4-dichlorobutane). Chlorine reactions with alkanes have diffusion-limited rate constants that do not depend on the molecular structure, indicating the absence of a potential barrier. Hydrogen abstraction from alcohols is slower than from alkanes and depends weakly on molecular structure, consistent with a small reaction barrier. Reactions with chlorinated alkanes are the slowest, and their rate constants depend strongly on the number and position of the chlorine substituents, signaling the importance of activation barriers to these reactions. The relative rate constants for the activation-controlled reactions agree very well with the predictions of the gas-phase structure-activity relationships.     

Far infrared and millimetre-wave absorption spectra of some low-loss polymers

Absorption spectra in the range 2–50 cm⁻¹ are reported for polyethylene, polypropylene and 'TPX' (basically poly 4-methyl pentene-1). The former has no resonances in this region and the continuum absorption can be represented by a simple quadratic function of wavenumber which, when extrapolated to radio frequencies, gives a good account of the observed losses. Polypropylene and 'TPX' show discrete absorption bands, but for these too there appears to be an underlying continuum. The millimetre-wave absorption possibly arises from a summation of the high frequency wings of the radio region relaxations and the low frequency wings of the far infrared resonances plus an inherent continuum which may be analogous to the broad absorption shown by non-polar liquids in the far infrared.