Vibrational Relaxation of D2O Induced by Collision with He: A Rigid Bender Close Coupling Study.

The vibrational relaxation of the first excited bending state of D2O induced by collision with He is studied at the close coupling level and using the Rigid Bender approximation. A new 4D potential energy surface is calculated and reported for this system. It is then used to determine the low-lying bound states of the D2O-He van der Waals complex and to perform scattering calculations. Collision rates are determined for pure rotational transitions as well as for rovibrational transitions within the first excited bending state. The results are compared with those obtained for the collision of D2O with other noble gases such as Ne and Ar. We also analyse the differences observed with respect to the H2O+He collisions and compare our results with experiment.

A new ab initio potential energy surface for the collisional excitation of O2 by H2.

We present a new four dimensional (4D) potential energy surface for the O(2)-H(2) system. Both molecules were treated as rigid rotors. Potential was obtained from the electronic structure calculations using a partially spin-restricted coupled cluster with the single, double and perturbative triple excitations [RCCSD(T)] method. The four atoms were described using the augmented correlation-consistent quadruple zeta (aug-cc-pVQZ) basis sets. Bond functions were placed at mid-distance between the O(2) center of mass and the center of mass of H(2) for a better description of the van der Waals interaction. Additionally, at five characteristic geometries, we calculated perturbational components of the interaction energy using the Symmetry-Adapted Perturbation Theory [SAPT] approach to explain the anisotropy of the potential energy surface. Bound states of the O(2)-H(2) van der Waals complex are computed using this potential. Close coupling calculations of the inelastic integral cross sections of O(2) in collisions with para-H(2) and ortho-H(2) were also calculated at low energies. After Boltzmann thermal averaging, rate coefficients were obtained for temperatures ranging from 5 to 100 K. No significant differences exist between para- and ortho-H(2) results.

Determinación del contenido de zinc en arroz y otros agroproductos por fluorescencia de rayos X / ZINC content determination in rice and other agriproducts by x-ray fluorescence

RESUMEN Se reporta el contenido de zinc en alimentos de consumo regular en Cuba (arroz, algunos vegetales y raíces comestibles). Las concentraciones se determinan por fluorescencia de rayos X empleando un juego de patrones de matriz orgánica dopados con zinc. La validación de la metodología analítica se realiza con los materiales de referencia certificados AIEA 393 y MAB3/ TM. Los resultados muestran al arroz como el producto agrícola de mayor bioacumulación de zinc, siendo la principal fuente de Zn en la dieta de la población cubana.

ABSTRACT The Zn content in foodstuffs (rice, some vegetables and roots) regularly consumed in Cuba is reported. Concentrations are determined by X-Ray Fluorescence analysis using a set of organic standards doped with Zn. The accuracy of the analytical procedure was validated using the Certified Reference Materials AIEA 393 and MAB3/ TM. The obtained results show rice as the major Zn bioaccumulator of the studied agriproducts and the main Zn source of human consumption in Cuba.