Orbital symmetry analysis of the reaction of silylenes with acetylenes and the dimerization of 1-silacyclopropenes

The addition of silylenes to acetylenes, and the dimerization of silacyclopropenes, are treated by Orbital Correspondence Analysis in Maximum Symmetry (OCAMS). The products observed in the latter reaction are consistent with an allowed pathway, a b_1g displacement involving rotation of the silacyclopropene molecules relative to one another in the transition state.     

Electronic transitions of polysilanes and their photochemistry

The photolytic fragmentation of trisilane to disilane and silylene has been studied by means of a pseudopotential method. The lower-lying electronically excited states in several of the silanes have been calculated and analysed with respect to their Rydberg character, with the inclusion of d orbitals. The effect of methylation on the stability of the silicon-silicon bond, as well as on the above photochemical model reaction, is discussed. An orbital correlation diagram with defined energy levels is presented.     

Reactions of CH3SH and (CH3)2S2 on the (0001) and (000) Surfaces of ZnO

Temperature-programmed desorption (TPD) was used to study the adsorption and reaction of CH3SH and (CH3)2S2 on the (0001) and (000) surfaces of ZnO. The interaction of these molecules with ZnO was found to be structure-sensitive. Both CH3SH and (CH3)2S2 adsorb dissociatively on ZnO(0001), forming adsorbed methylthiolate intermediates and only molecularly on ZnO(000). In the case of CH3SH, this result is consistent with that reported previously for the interaction of Br?nsted acids with ZnO and indicates that exposed cation-anion pairs are the active sites for dissociative adsorption. Only exposed Zn cations are required for the dissociative adsorption of (CH3)2S2. Methylthiolate species produced by dissociative adsorption of CH3SH and (CH3)2S2 on ZnO(0001) were found to undergo a variety of reaction pathways, including coupling to produce dimethyl sulfide and oxidation to formaldehyde, CO, and CO2. Pathways for the production of these various products are proposed.     

A qualitative determination of the favourable nuclear pathway for the ground state decomposition of formyl-fluoride

A qualitative, symmetry-independent, procedure is applied to the thermal decomposition of formyl-fluoride in order to single out energetically favourable directions on the potential energy surface for its fragmentation to carbon monoxide and hydrogen fluoride. The qualitative results are in good agreement with published calculations for the favoured decomposition pathway and compatible with experimental results.     

Symmetry analysis of the potential energy surfaces for the photochemical decomposition of formaldehyde

Orbital Correspondence Analysis in Maximum Symmetry (OCAMS) is applied to the decomposition pathways of formaldehyde to H₂ + CO and to H + HCO. The symmetry adapted nuclear motions, which are preferentially incorporated in the energetically favoured fragmentation pathways on both the ground and excited state surfaces are singled out. The results of this analysis are in full agreement with those of published potential energy surfaces and consistent with the results of experimental investigations reported in the literature. The nuclear motions favouring the various processes thus appear to be deducible from considerations of orbital symmetry.This work was carried out during tenure of a Minerva Foundation grant to one of us. (E.A.H.)     

Aerosol-derived Ni(1-x)Zn(x) electrocatalysts for direct hydrazine fuel cells

This article reports the synthesis and performance of unsupported Ni(1-x)Zn(x) electrocatalysts for the oxidation of hydrazine in alkaline media. Characterization of these catalysts was achieved using XRD, SEM, and TEM to confirm phase compositions, crystal structures, and morphologies. High performance was observed for the α-Ni(0.87)Zn(0.13) and β(1)-Ni(0.50)Zn(0.50) electrocatalysts with an onset potential of -0.15 V (vs. RHE) and a mass activity of 4000-3800 A g(cat)(-1) at 0.4 V (vs. RHE), respectively. Additionally, in situ IRRAS studies were conducted to understand the mechanism of oxidation. These results demonstrate the feasibility of Ni(1-x)Zn(x) catalysts for direct hydrazine anionic fuel cells.