The optical activity of carvone: a theoretical and experimental investigation

The optical rotatory dispersion (ORD) and circular dichroism of the conformationally flexible carvone molecule has been investigated in 17 solvents and compared with results from calculations for the "free" (gas phase) molecule. The G3 method was used to determine the relative energies of the six conformers. The optical rotation of (R)-(-)-carvone at 589 nm was calculated using coupled cluster and density functional methods, including temperature-dependent vibrational corrections. Vibrational corrections are significant and are primarily associated with normal modes involving the stereogenic carbon atom and the carbonyl group, whose n → π? excitation plays a significant role in the chiroptical response of carvone. Without the inclusion of vibrational corrections the optical rotation calculated with CCSD and DFT has the opposite sign of experimental data. Calculations of optical rotation performed in solution using the polarizable continuum model were also opposite in sign when compared to that of the experiment.     

Deformation properties of the neutron-deficient odd-A Pt and Hg nuclei

Nuclear and atomic spectroscopy measurements have provided a great number of data on the neutron-deficient Pt and Hg nuclei. The odd-A Pt and Hg with A<186 have a prolate shape, and the even-even isotopes have a triaxial shape, while the nuclear shape of the odd-A Pt and Hg with A>186 is still an open question. The energy of the low-lying levels and the nuclear moments have been calculated in the framework of a semimicroscopic “axial-rotor + 1 quasiparticle” coupling model. The predictions are compared with the experimental data and discussed. The results strongly suggest a prolate shape for the negative-parity low-lying states of the odd-A ^187–191Pt and ^187–193Hg isotopes.     

A model to set measurement quality objectives and to establish measurement uncertainty expectations in analytical chemistry laboratories using ASTM proficiency test data

A model is presented that correlates historical proficiency test data as the log of interlaboratory standard deviations versus the log of analyte concentrations, independent of analyte (measurand) or matrix. Analytical chemistry laboratories can use this model to set their internal measurement quality objectives and to apply the uncertainty budget process to assign the maximum allowable variation in each major step in their bias-free measurement systems. Laboratories that are compliant with this model are able to pass future proficiency tests and demonstrate competence to laboratory clients and ISO 17025 accreditation bodies. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/ 10.1007/s007690100398-y. Received: 31 March 2001 Accepted: 11 September 2001     

Deformation change in light iridium nuclei from laser spectroscopy

Laser spectroscopy measurements have been performed on neutron-deficient and stable Ir isotopes using the COMPLIS experimental setup installed at ISOLDE-CERN. The radioactive Ir atoms were obtained from successive decays of a mass-separated Hg beam deposited onto a carbon substrate after deceleration to 1kV and subsequently laser desorbed. A three-color, two-step resonant scheme was used to selectively ionize the desorbed Ir atoms. The hyperfine structure (HFS) and isotope shift (IS) of the first transition of the ionization path 5d ⁷6s ²⁴ F _9/2 → 5d ⁷6s6p ⁶ F _11/2 at 351.5nm were measured for ^182-189Ir, ¹⁸⁶Ir ^m and the stable ^{191, 193}Ir. The nuclear magnetic moments μ_I and the spectroscopic quadrupole moments Q_s were obtained from the HFS spectra and the change of the mean square charge radii from the IS measurements. The sign of μ_I was experimentally determined for the first time for the masses 182≤A≤189 and the isomeric state ¹⁸⁶Ir ^m . The spectroscopic quadrupole moments of ¹⁸²Ir and ¹⁸³Ir were measured also for the first time. A large mean square charge radius change between ¹⁸⁷Ir and ¹⁸⁶Ir ^g and between ¹⁸⁶Ir ^m and ¹⁸⁶Ir ^g was observed corresponding to a sudden increase in deformation: from β₂ ≃ + 0.16 for the heavier group A = 193, 191, 189, 187 and 186m to β₂≥ + 0.2 for the lighter group A = 186g, 185, 184, 183 and 182. These results were analyzed in the framework of a microscopic treatment of an axial rotor plus one or two quasiparticle(s). This sudden deformation change is associated with a change in the proton state that describes the odd-nuclei ground state or that participates in the coupling with the neutron in the odd-odd nuclei. This state is identified with the π3/2⁺[402] orbital for the heavier group and with the π1/2^-[541] orbital stemming from the 1h _9/2 spherical subshell for the lighter group. That last state seems to affect strongly the observed values of the nuclear moments.     

Femtosecond laser-based fabrication of a new model material to study fracture

The ductile fracture process consists of the nucleation, growth and coalescence of voids in a material. Predictive models of ductility require a complete understanding of the coalescence event. However, coalescence occurs over very small strains and is therefore difficult to observe experimentally. We have addressed this by developing a new class of model material. It consists of femtosecond laser drilled holes and diffusion bonded metallic sheets, which can be mechanically tested in situ either by scanning electron microscopy (SEM) or by X-raycomputed tomography (XRCT). The fabrication steps are presented and the model material is characterized by optical and electron microscopy, nanoindentation and tomography. The heat affected zone around the laser holes is found to be harder than the unaffected material and consists of nano-scale grains. Finally we show that the coalescence event is well captured using both SEM and XRCT. The fabrication method is adaptable to a wide range of materials and enables one to produce 2D and 3D arrays of holes or cracks with controlled size, volume fraction and distribution. PACS  62.20.Mk; 62.25.+g; 79.20.Ds