Investigation of the Abstraction and Dissociation Mechanism in the Nitrogen Trifluoride Channels: Combined Post-Hartree-Fock and Transition State Theory Approaches.

The present paper concludes our series of kinetics studies on the reactions involved in the complex mechanism of nitrogen trifluoride decomposition. Two other related reactions that, along with this mechanism, take part in an efficient boron nitride growth process are also investigated. We report results concerning two abstraction reactions, namely NF2 + N ⇄ 2NF and NF3 + NF ⇄ 2NF2, and two dissociations, N2F4 ⇄ 2NF2 and N2F3 ⇄ NF2 + NF. State-of-the-art electronic structure calculations at the CCSD(T)/cc-pVTZ level of theory were considered to determine geometries and frequencies of reactants, products, and transition states. Extrapolation of the energies to the complete basis set limit was used to obtain energies of all the species. We applied transition state theory to compute thermal rate constants including Wigner, Eckart, Bell, and deformed theory corrections in order to take tunneling effects into account. The obtained results are in good agreement with the experimental data available in the literature and are expected to provide a better phenomenological understanding of the NF3 decomposition role in the boron nitride growth for a wide range of temperature values.

Reproductive dormancy in boll-weevil from populations of the midwest of Brazil.

The boll weevil (Anthonomus grandis Boheman) (Coleoptera: Curculionidae) is an introduced pest in Brazil, which in 30 yr has successfully expanded to various eco-regions and became the most important pest of cotton (Gossypium hirsutum, Malvaceae). Given the limited knowledge about the adaptive mechanisms that allowed successful establishment of the pest population in a tropical region, in this work we studied the potential of the Midwest population of boll weevils to enter a reproductive dormancy and identified the importance of the feeding source for induction of dormancy. We investigated morphological and physiological characters as indicators of the dormancy. We also investigated the occurrence of reproductive dormancy in boll weevils populations from cotton farms of the Midwestern region of Brazil during the cotton and noncotton seasons of 2009 and 2010. The studies revealed that boll weevils entered facultative reproductive dormancy; however, unlike what has been observed for boll weevils from temperate and subtropical regions, the hypertrophy of fat body and hexamerin levels did not straightly correlated to reproductive dormancy. The food source and field conditions during early adult development were decisive factor for the induction of reproductive dormancy. The incidence of reproductive dormancy increased progressively as the phenology of cotton plant advanced, reaching approximately 90% at the end of the crop season. During the noncotton season, the boll weevil was predominantly found in reproductive dormancy, especially females; however, there is evidence of use of multiple adaptive strategies to colonize the next harvest.