Early experiments with slow positrons in atomic physics

The major steps in the evolution of techniques for producing positron beams of well defined energies over the last 25 years are reviewed. Developments in the methods of using these beams for experiments in atomic physics are then traced historically     

Freedom and trying: Understanding agent-causal exertions

In this paper, I argue that trying is the locus of freedom and moral responsibility. Thus, any plausible view of free and responsible action must accommodate and account for free tryings. I then consider a version of agent causation whereby the agent directly causes her tryings. On this view, the agent is afforded direct control over her efforts and there is no need to posit—as other agent-causal theorists do—an uncaused event. I discuss the potential advantages of this sort of view, and its challenges.     

Neutron activation analysis of final molasses from Cuban sugar industry

Thermal and epithermal non-destructive activation analyses have been performed on samples of final molasses from 14 different sugar factories, covering the most important regions in Cuba. From the first measurement after irradiation at the Triga Mark reactor (VTT), the concentration of more than 15 elements is reported. The almost constant elemental composition shows that they can be used equally for different purposes as animal foodstuff and for the manufacture of biotechnological products. This work is part of a research project developed in order to establish a complete characterization of Cuban sugar molasses.     

Vibrational spectra of nitrido and oxo complexes

The vibrational spectra of a number of transition-metal complexes containing terminal or bridging nitrido (N^3?) and oxo (O^2?) ligands are reported. Full assignments of fundamental modes are given for (OsO₃¹⁴N)^?, (OsO₃¹⁵N)^?, (Os¹⁴NX₄)^?, (Os¹⁵NX₄)^?, (Ru¹⁴NX₄)^?, (Os¹⁴NX₅)^2?, (Os¹⁵NX₅)^2? and (Ru¹⁴NX₅)^2? (X = Cl, Br), and also for the oxo complexes (Mo¹⁶OCl₄, (Mo¹⁸OCl₄)^?, (Mo¹⁶OCl₅)^2? and (Mo¹⁸OCl₅)^2?. Force constants have been evaluated for the four- and five-coordinate complexes. The significance of the results is discussed in terms of the metalligand bonding involved in these species.     

Towards novel difluorinated sugar mimetics; syntheses and conformational analyses of highly-functionalised difluorinated cyclooctenones

Highly-functionalised difluorinated cyclooctenones were synthesised from trifluoroethanol using either metallated difluoroenol acetal or carbamate chemistry, followed by a [2,3]-Wittig rearrangement or aldol reaction. Efficient RCM reactions afforded the title compounds which showed rather restricted fluxional behaviour by VT (19)F NMR. Topological characterisation by molecular modelling and NOESY/ROESY experiments offered a number of challenges, but allowed the identification of two favoured boat-chair conformers which interconverted by pseudorotation with relatively large activation barriers.     

On the role of solvent in complexation equilibria. I. The acid-base chemistry of some α,ω-diaminocarboxylic acids in water-dioxane mixed solvents

The macroscopic and microscopic acid-base chemistry of a series of α,ω-diaminocarboxylic acids, H₂N(CH₂)_nCH(NH₂)COOH [n=4, lysine (LYS);n=3, ornithine (ORN);n=2, 2,4-diaminobutyric acid (DAB);n=1, 2,3-diaminopropionic acid (DAP)], was determined in water and its binary mixtures with dioxane (20.5, 40.7, 60.7, and 80.5 mass % dioxane) using carbon-13 nuclear magnetic resonance spectroscopy. The macroscopic acid dissociation constants for the titration of the two ammonium groups decrease uniformly with increasing dioxane composition. The microscopic constants, however, which characterize the relative concentrations of the two tautomers of singly protonated amino acid (I and II) $$\begin{gathered} H_3 \mathop N\limits^ + (CH_2 )_n CHCOO^ - H_2 N(CH_2 )_n CHCOO^ - \hfill \\ || \hfill \\ NH_2 \mathop N\limits_ + H_3 \hfill \\ III \hfill \\ \end{gathered}$$ reveal that while tautomer I is favored in aqueous solution, tautomer II becomes more important with increasing dioxane composition for LYS and ORN. The relative concentrations of I and II remain unchanged with solvent composition for DAP. These results are explained in terms solute-solvent and solvent-solvent interactions.     

Matrix-isolation-FTIR spectroscopy with an integrating sphere

The use of an integrating sphere for the measurement of absorption spectra of thin films is described. The thin film (for example a rare gas matrix) is grown directly on the inside surface of the sphere. Multiple reflections inside the integrating sphere lead to significant enhancement of weak absorptions of the film, increasing the sensitivity of such measurements.     

DEPTH RESOLUTION IN PHOTOELECTRON MICROSCOPY OF ORGANIC SURFACES. THE PHOTOELECTRIC EFFECT OF PHTHALOCYANINE THIN FILMS

Abstract— The application of photoelectron microscopy as a general method of imaging organic and biological surfaces requires a knowledge of the photoelectric effect of very thin organic films. In this study, low magnification images of a 7 Å thick pattern of copper phthalocyanine were obtained, demonstrating that it is possible to visualize a monolayer of organic compound in photoelectron microscopy. Relative photoelectron currents were measured for a series of copper phthalocyanine films ranging in thickness up to 1900 Å. The relative photoelectron currents were independent of temperature (90–298°K), suggesting that electron-electron and not electron-phonon scattering is the dominant mechanism. The photoelectric properties measured are determined primarily by the large organic ring structure and not the central metal atom, as evidenced by the fact that substitution of metal-free phthalocyanine for copper phthalocyanine did not substantially alter the values of observed photoelectron currents. An analysis of the data indicates the depth resolution is 15 ű 5 Å, and equals the electron mean free path. This very good depth resolution is a result of the low kinetic energy associated with electrons released by irradiation near the photoemission threshold.