Ab initio investigation of intermolecular interactions in solid benzene

A computational strategy for the evaluation of the crystal lattice constants and cohesive energy of the weakly bound molecular solids is proposed. The strategy is based on the high level ab initio coupled-cluster determination of the pairwise additive contribution to the interaction energy. The zero-point-energy correction and non-additive contributions to the interaction energy are treated using density functional methods. The experimental crystal lattice constants of the solid benzene are reproduced, and the value of 480 meV/molecule is calculated for its cohesive energy

Near-dissociation states and coupled potential curves for the HeN+ complex

The near-dissociation microwave rovibronic spectra of HeN+ [Carrington et al., Chem. Phys. Lett. 262, 598 (1996)] are used to obtain coupled potential energy curves for the six electronic states correlating with He+N+ 3P0, 3P1, and 3P2. High-quality ab initio calculations are carried out, using a spin-restricted open-shell coupled-cluster method with an augmented correlation-consistent quintuple-zeta basis set (aug-cc-pV5Z). Fully coupled calculations of bound and quasibound states are performed, including all six electronic states, and suggest two possible assignments of the observed transitions. The potentials are then morphed (scaled) to reproduce the experimental frequencies. One of the two assignments, designated SH1, is preferred because it gives a more satisfactory explanation of the observed hyperfine splittings. The corresponding morphed potential has well depths of 1954 cm−1 and 192 cm−1 for the spin-free 3Σ− and 3Π curves, respectively

Efficient Stark deceleration of cold polar molecules

Stark deceleration has been utilized for slowing and trapping several species of neutral, ground-state polar molecules generated in a supersonic beam expansion. Due to the finite physical dimension of the electrode array and practical limitations of the applicable electric fields, only molecules within a specific range of velocities and positions can be efficiently slowed and trapped. These constraints result in a restricted phase space acceptance of the decelerator in directions both transverse and parallel to the molecular beam axis; hence, careful modeling is required for understanding and achieving efficient Stark decelerator operation. We present work on slowing of the hydroxyl radical (OH) elucidating the physics controlling the evolution of the molecular phase space packets both with experimental results and model calculations. From these results we deduce experimental conditions necessary for efficient operation of a Stark decelerator.Comment: 8 pages, 9 figure

La agricultura andina ante una globalización en desplome

Casi toda la discusión que se da hoy en día en el Perú acerca del desarrollo agrícola se basa en la presunción de que el mundo del futuro será simplemente una extensión del mundo de hoy. Se cree que el proceso de globalización va a seguir avanzando con el mismo rumbo que los últimos veinte o treinta años. Se supone también que la agricultura peruana siempre contará con mercados extranjeros en permanente crecimiento, en los cuales se podrán colocar los productos nacionales y de donde se importarán productos baratos necesarios para satisfacer las necesidades alimenticias que no se producen aquí o cuya producción no se considera económicamente competitiva en la coyuntura. Se predica así el desarrollo prioritario de una agricultura altamente tecnificada para la producción de bienes para la exportación, que también servirá para el mercado urbano nacional

Cold collisions of OH and Rb. I: the free collision

We have calculated elastic and state-resolved inelastic cross sections for cold and ultracold collisions in the Rb($^1 S$) + OH($^2 \Pi_{3/2}$) system, including fine-structure and hyperfine effects. We have developed a new set of five potential energy surfaces for Rb-OH($^2 \Pi$) from high-level {\em ab initio} electronic structure calculations, which exhibit conical intersections between covalent and ion-pair states. The surfaces are transformed to a quasidiabatic representation. The collision problem is expanded in a set of channels suitable for handling the system in the presence of electric and/or magnetic fields, although we consider the zero-field limit in this work. Because of the large number of scattering channels involved, we propose and make use of suitable approximations. To account for the hyperfine structure of both collision partners in the short-range region we develop a frame-transformation procedure which includes most of the hyperfine Hamiltonian. Scattering cross sections on the order of $10^{-13}$ cm$^2$ are predicted for temperatures typical of Stark decelerators. We also conclude that spin orientation of the partners is completely disrupted during the collision. Implications for both sympathetic cooling of OH molecules in an environment of ultracold Rb atoms and experimental observability of the collisions are discussed.Comment: 20 pages, 16 figure

Acceptance and uptake of improved biomass cookstoves in Peru: learning from system level approaches to transform large-scale cooking interventions

Improved biomass cookstoves (ICS) are cooking technologies that increase wellbeing and reduce household air pollution. With the goal of identifying factors influencing ICS acceptance and uptake at five system levels (intrapersonal, interpersonal, community, institutional, and policy), we carried out a qualitative study in three regions in Peru. We conducted 32 focus group discussions (243 ICS users) and 26 semi-structured interviews with key stakeholders, applying a combination of two system-level frameworks for analysis: the socio-ecological model and the ICS adoption domain. Enabling and impeding factors at each level were closely related to each other. Decisions made by policy makers - often centralised and not considering local/regional realities - strongly influenced acceptance and barriers at lower levels. ICS acceptance and uptake tended to be low when ICS users were not involved from the start. Most ICS programmes focused on stove distribution outputs, without considering community needs, such as training on ICS building, maintenance and repair, or issues related to spare part availability, which is a strong barrier to sustained uptake of ICS. Using a combination of models that allows one to examine facilitators and barriers at multiple levels, as well as the interactions of those levels, was useful in assessing potential improvements to intervention design, facilitating programme success, preventing unforeseen programme adaptations, and improving cost-effectiveness of interventions

Spectroscopy of Na⁺．Rg and transport coefficients of Na⁺ in Rg(Rg＝He ―Rn)

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Three-body non-additive forces between spin-polarized alkali atoms

Three-body non-additive forces in systems of three spin-polarized alkali atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio calculations. The non-additive forces are found to be large, especially near the equilateral equilibrium geometries. For Li, they increase the three-atom potential well depth by a factor of 4 and reduce the equilibrium interatomic distance by 0.9 A. The non-additive forces originate principally from chemical bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files