Self-assembled growth of nanostructural Ge islands on bromine-passivated Si(111) surfaces at room temperature

We have deposited relatively thick (∼60 nm) Ge layers on Br-passivated Si(111) substrates by thermal evaporation under high vacuum conditions at room temperature. Ge has grown in a layer-plus-island mode although it is different from the Stranski-Krastanov growth mode observed in epitaxial growth. Both the islands and the layer are nanocrystalline. This appears to be a consequence of reduction of surface free energy of the Si(111) substrate by Br-passivation. The size distribution of the Ge nanoislands has been determined. The Br-Si(111) substrates were prepared by a liquid treatment, which may not produce exactly reproducible surfaces. Nevertheless, some basic features of the nanostructural island growth are reasonably reproducible, while there are variations in the details of the island size distribution.     

Coulomb excitation of the odd-odd isotopes 106, 108In

The low-lying states in the odd-odd and unstable isotopes ^{106, 108}In have been Coulomb excited from the ground state and the first excited isomeric state at the REX-ISOLDE facility at CERN. With the additional data provided here the $ \pi$ g _9/2 ^-1 ? $ \nu$ d _5/2 and $ \pi$ g _9/2 ^-1 ? $ \nu$ g _7/2 multiplets have been re-analyzed and are modified compared to previous results. The observed $ \gamma$ -ray de-excitation patterns were interpreted within a shell model calculation based on a realistic effective interaction. The agreement between theory and experiment is satisfactory and the calculations reproduce the observed differences in the excitation pattern of the two isotopes. The calculations exclude a 6⁺ ground state in ¹⁰⁶In . This is in agreement with the conclusions drawn using other techniques. Furthermore, based on the experimental results, it is also concluded that the ordering of the isomeric and ground state in ¹⁰⁸In is inverted compared to the shell model prediction. Limits on B(E2) values have been extracted where possible. A previously unknown low-lying state at 367keV in ¹⁰⁶In is also reported.     

Gas-phase reactivity of lactones: structure and stability of their Cu+ complexes

The structure and relative stability of different lactone-Cu⁺ complexes, including cycles changing from four to six-membered rings, have been investigated through the use of density functional theory methods. The geometries and vibrational frequencies were calculated at the B3LYP/6-311G(d,p) level. Final energies were obtained in single point calculations carried out at the B3LYP/6-311+G(2df,2p) level of theory. Upon interaction with Cu⁺ in the gas phase, lactones behave in a rather similar way as they do in protonation processes. Systematically the global minimum of the potential energy surface corresponds to the attachment of the metal cation to the carbonyl oxygen cis with respect to the ether-like oxygen. Also, similarly to proton affinities, the calculated Cu⁺ binding energies increase with the size of the system. The unsaturated compounds are found to be only slightly more basic than the saturated counterparts. Cu⁺ attachment leads to significant bond activation and bond reinforcement effects, reflected in redshiftings and blueshiftings of the stretching frequencies, respectively. Cu⁺ is able to form agostic bonds with some of the CH² groups of the lactone moiety. These agostic complexes can be good precursors for the unimolecular loss of H², which very likely should be observed in the mass spectra.     

The reactions of Cl+ (3P) and Cl+ (1D) with hydrogen sulphide. A G2 molecular orbital study

G2 ab initio molecular orbital calculations have been performed to study the potential energy surfaces (PESs) associated with the reactions of Cl⁺ in its ³P ground state and in its ¹D first excited state with hydrogen sulphide. [H₂, Cl, S]⁺ singlet and triplet state cations present very different bonding characteristics. The latter are systematically ion-dipole or hydrogen-bonded weakly bound species, while the former are covalent molecular ions. As a consequence, although the Cl⁺(³P) is 34.5 kcal mol^?1 more stable than Cl⁺(¹D), the global minimum of the singlet PES lies 37.3 kcal mol^?1 below the global minimum of the triplet PES. Both singlet and triplet potential energy surfaces show significant differences with respect to those associated with Cl⁺ + H₂O reactions as well as with SH₂ reactions with F⁺. In both cases, the major product should be SH⁺ ₂; SH⁺ and HCl⁺ being the minor products, in agreement with the experimental evidence. The estimated heat of formation for the most stable H₂SCl⁺ singlet state species is 198 ± 1 kcal mol^?1.