How the addition of atomic hydrogen to a multiple bond can be catalyzed by water molecules.

Observational data show complex organic molecules in the interstellar medium (ISM). Hydrogenation of small unsaturated carbon double bond could be one way for molecular complexification. It is important to understand how such reactivity occurs in the very cold and low-pressure ISM.

The significant role of water in reactions occurring on the surface of interstellar ice grains: Hydrogenation of pure ketene HCCO ice hydrogenation of mixed HCCO/HO ice at 10 K.

Water ice plays an important role in reactions taking place on the surface of interstellar ice grains, ranging from catalytic effects that reduce reaction barrier heights to effects that stabilize the reaction products and intermediates formed, or that favor one reaction pathway over another, passing through water-involvement in the reaction to produce more complex molecules that cannot be formed without water or water-derived fragments H, O and OH. In this context, we have combined experimental and theoretical studies to investigate ketene (CHCO) + H solid-state reaction at 10 K in the presence and absence of water molecules under interstellar conditions, through H-bombardment of CHCO and CHCO/HO ices. We show in the present study that with or without water, the ketene molecule reacts with H atoms to form four reaction products, namely CO, HCO, CH and CHCHO.

Formation of CO, CH, HCO and CHCHO through the HCCO + H surface reaction under interstellar conditions.

The reaction of ketene (HCCO) with hydrogen atoms has been studied under interstellar conditions through two different experimental methods, occurring on the surface and in the bulk of HCCO ice. We show that ketene interaction with H-atoms at 10 K leads mainly to four reaction products, carbon monoxide (CO), methane (CH), formaldehyde (HCO) and acetaldehyde (CHCHO). A part of these results shows a chemical link between a simple organic molecule such as HCCO and a complex one such as CHCHO, through H-addition reactions taking place in dense molecular clouds.

Composition dependent reactivity of titanium oxide clusters.

Based on first-principles calculations of titanium oxide clusters, TinOm (n = 1-4), we reveal the composition dependent reactivity of titanium oxide clusters. Our interesting results include: (1) the reactivity depends on the ratio of O atoms in the clusters, with smaller O ratios associated with higher reactivity; (2) among the different titanium oxide species investigated, the most stable structures are TinO2n, but their reactivities are relatively lower than the clusters with a smaller O atom ratio; moreover, (3) when the O atom ratio is small, the reactivity required to form the Ti-Ti bond is larger than either the Ti-O or O-O bond between two interacting titanium oxide clusters. These results will be useful for designing efficient titanium oxide catalysts, or photocatalysts, in particular, for energy and environmental applications.

CO dissociation on magnetic Fe(n) clusters.

This work theoretically investigates the CO dissociation on Fen nanoparticles, for n in the range of 1-65, focusing on size dependence in the context of the initial step of the Fischer-Tropsch reaction. CO adsorbs molecularly through its C-end on a triangular facet of the nanoparticle. Dissociation becomes easier when the cluster size increases.

Modeling localized photoinduced electrons in rutile-TiO2 using periodic DFT+U methodology.

We propose a theoretical model for photocatalytic processes on titanium dioxide, described by its most stable phase and surface, rutile-TiO(2)(110). The excitation induced by light promotes electrons from the valence band to the conduction band. In this context, one important requirement is having a correct value of the magnitude of the electronic gap.