Photoelectron He(I) Spectra of small silanes

The photoelectron He(I) spectra of methyl-, dimethyl-, trimethyl- and ethylsiliane are reported and assigned with the help of CNDO/2 calculations.For each silane the ordering of the valence MO's obtained from calculations is, very close to that of the corresponding alkane, and is in agreement with spectral evidence. Participation of silicon d orbitals in bonding is not substantial but is more important in the outermost SiC and SiH MO's than in the π MO's mainly localized on the alkyl groups.     

On the possibility of using model potentials for collision integral calculations of interest for planetary atmospheres

The interaction energy in systems (atom–atom, atom–ion and atom–molecule) involving open-shell species, predicted by a phenomenological method, is used for collision integral calculations. The results are compared with those obtained by different authors by using the complete set of quantum mechanical interaction potentials arizing from the electronic configurations of separate partners. A satisfactory agreement is achieved, implying that the effect of deep potential wells, present in some of the chemical potentials, is cancelled by the effect of strong repulsive potentials.     

Weighted Composition Operators from H ∞ to the Bloch Space of a Bounded Homogeneous Domain

Let D be a bounded homogeneous domain in ℂ ⁿ . In this paper, we study the bounded and the compact weighted composition operators mapping the Hardy space H ^∞(D) into the Bloch space of D. We characterize the bounded weighted composition operators, provide operator norm estimates, and give sufficient conditions for compactness. We prove that these conditions are necessary in the case of the unit ball and the polydisk. We then show that if D is a bounded symmetric domain, the bounded multiplication operators from H ^∞(D) to the Bloch space of D are the operators whose symbol is bounded.     

Short-range exchange and correlation energy density functionals: beyond the local-density approximation

We propose approximations which go beyond the local-density approximation for the short-range exchange and correlation density functionals appearing in a multideterminantal extension of the Kohn-Sham scheme. A first approximation consists of defining locally the range of the interaction in the correlation functional. Another approximation, more conventional, is based on a gradient expansion of the short-range exchange-correlation functional. Finally, we also test a short-range generalized-gradient approximation by extending the Perdew-Burke-Ernzerhof exchange-correlation functional to short-range interactions.     

Characterization of starch polysaccharides by flow field-flow fractionation-multi-angle laser light scattering-differential refractometer index

The coupling between flow field-flow fractionation (FFF), multi-angle laser light scattering and differential refractometer index provides a promising technique for fractionation of starch polysaccharides in aqueous conditions. Native starches with different amylose/amylopectin levels (0-70%) as well as a pure amylose sample were characterized. By applying a sudden drop in the cross-flow-rate, clear separation was achieved between amylose (which elutes first) and amylopectin. Flow FFF produced correct relationships between the molecular mass or the gyration radius versus elution volume for the fractionated amylopectin population. The results are also considered in terms of the macromolecular composition of starches.     

Enantioselective reactions catalyzed by synthetic enzymes. A model for chemical evolution

Polyleucines of various lengths act as enantioselective catalysts in the aldol condensation between cyclohexanone and various aromatic aldehydes. Polyleucine and other polyamino acids behave as synthetic enzymes in the epoxidation of chalcone and other electron-deficient alkenes. Both reactions are of considerable prebiotic significance.     

Photoelectron spectra of 1,4-dithiin and related compounds

The photoelectron (He(I)) spectra of 1,4-dithiin (1), 1,4-thiaselenin (2), 1,4-thiatellurin (3) and 4H-thiopyran (4) were assigned by comparison with published spectra of similar compounds and with the help of ab initio and semi-empirical calculations. The proposed orbital sequences for the outermost orbitals are π₄, π₃, π₂, σ for 1, 2 and 3, and π₄, π₂, σ, π₃ for 4. π₄ and π₃ correspond to the symmetric and antisymmetric combinations, respectively, of the heteroatom lone pairs, while π₂ is the antisymmetric combination of the π_eth orbitals.