Low energy H+CO scattering revisited - CO rotational excitation with new potential surfaces

Context. A recent modeling study of brightness ratios for CO rotational transitions in gas typical of the diffuse ISM by Liszt found the role of H collisions to be more important than previously assumed. This conclusion was based on recent quantum scattering calculations using the so-called WKS potential energy surface (PES) which reported a large cross section for the important 0 → 1 rotational transition. This result is in contradiction to one obtained using the earlier BBH PES for which the cross section is quite small and which is consistent with an expected homonuclear-like propensity for even ∆J transitions. Aims. We revisit this contradiction with new scattering calculations using two new ab initio PESs that focus on the important long- range behavior and explore the validity of the apparent departure from the expected even ∆J propensity in H-CO rotational excitation obtained with the WKS PES. Methods. Close-coupling (CC) rigid-rotor calculations for CO(v = 0, J = 0) excitation by H are performed on four different PESs. Two of the PESs are obtained in this work using state-of-the-art quantum chemistry techniques at the CCSD(T) and MRCI levels of theory. Results. Cross sections for the J = 0 → 1, as well as other odd ∆J, transitions are significantly suppressed compared to even ∆J transitions in thermal energy CC calculations using the CCSD(T) and MRCI surfaces. This is consistent with the expected even ∆J propensity and in contrast to CC calculations using the WKS PES which predict a dominating 0 → 1 transition. Conclusions. Inelastic collision cross section calculations are sensitive to fine details in the anisotropic components of the PES and its long-range behavior. The current results obtained with new surfaces for H-CO scattering suggest that the original astrophysical assumption that excitation of CO by H2 dominates the kinetics of CO in diffuse ISM gas is likely to remain valid

Interaction of Hydrogen with Graphitic Surfaces, Clean and Doped with Metal Clusters

Producción CientíficaHydrogen is viewed as a possible alternative to the fossil fuels in transportation. The technology of fuel-cell engines is fully developed, and the outstanding remaining problem is the storage of hydrogen in the vehicle. Porous materials, in which hydrogen is adsorbed on the pore walls, and in particular nanoporous carbons, have been investigated as potential onboard containers. Furthermore, metallic nanoparticles embedded in porous carbons catalyze the dissociation of hydrogen in the anode of the fuel cells. For these reasons the interaction of hydrogen with the surfaces of carbon materials is a topic of high technological interest. Computational modeling and the density functional formalism (DFT) are helping in the task of discovering the basic mechanisms of the interaction of hydrogen with clean and doped carbon surfaces. Planar and curved graphene provide good models for the walls of porous carbons. We first review work on the interaction of molecular and atomic hydrogen with graphene and graphene nanoribbons, and next we address the effects due to the presence of metal clusters on the surface because of the evidence of their role in enhancing hydrogen storage.Ministerio de Economía, Industria y Competitividad (Grant MAT2014-54378-R

Edge configurational effect on band gaps in graphene nanoribbons

In this article, we put forward a resolution to the prolonged ambiguity in energy band gaps between theory and experiments of fabricated graphene nanoribbons (GNRs). Band structure calculations using density functional theory are performed on oxygen-passivated GNR supercells of customized edge configurations without disturbing the inherent sp(2) hybridization of carbon atoms. Direct band gaps are observed for both zigzag and armchair GNRs, consistent with the experimental reports. In addition, we provide an explanation of the experimentally observed scattered band gap values of GNRs as a function of width in a crystallographic orientation on the basis of edge configurations. We conclude that edge configurations of GNRs significantly contribute to band gap formation in addition to its width for a given crystallographic orientation and will play a crucial role in band gap engineering of GNRs for future research on fabrication of nanoelectronic devices

Ty3/Gypsy retrotransposons in the Pacific abalone Haliotis discus hannai: characterization and use for species identification in the genus Haliotis

Transposable elements are highly abundant elements that are present in all eukaryotic species. Here, we present a molecular description of abalone retrotransposon (Abret) elements. The genome of Haliotis discus hannai contains 130 Abret elements which were all Ty3/Gypsy retrotransposons. The Ty1/Copia elements were absent in the H. discus hannai genome. Most of the elements were not complete due to sequence truncation or coding region decay. However, three elements Abret-296, Abret-935, and Abret-3259 had most of the canonical features of LTR (long terminal repeat)-retrotransposons. There were several reading frame shifts in Abret-935 and Abret-3259 elements. Surprisingly, phylogenetic analysis indicated that all of the elements belonged to the Osvaldo lineage. The sequence divergence between LTRs revealed that the Abret elements were mostly active within 2 million years ago. Abret elements were used as molecular markers in SSAP analyses, which allowed clear distinction of different species in the genus Haliotis. The polymorphic markers were converted into SCAR markers for use in species identification by simple PCR in the Haliotis genus