ALBERT

Notes: The processes by which solvated electrons are generated and undergo recombination are of great interest in condensed phase physical chemistry because of their relevance to both electron transfer reactions and radiation chemistry. Although most of the work in this area has focused on aqueous systems, many outstanding questions remain, especially concerning the nature of these processes in low polarity solvents where the solvated electron has a fundamentally different structure. In this paper, we use femtosecond spectroscopic techniques to explore the dynamics of solvated electrons in tetrahydrofuran (THF) that are produced in two different ways: ejection by multiphoton ionization of the neat solvent, and detachment via the charge-transfer-to-solvent (CTTS) transition of sodide (Na−). Following multiphoton ionization of the solvent, the recombination of solvated electrons can be well described by a simple model that assumes electrons are first ejected to a given thermalization distance and then move diffusively in the presence of the Coulombic attraction with their geminate cation. The short-time transient absorption dynamics of the THF radical cation in the visible region of the spectrum do not match the kinetics of the solvated electron probed at ∼2 μm, indicating that caution is warranted when drawing conclusions about recombination based only on the dynamics of the solvent cation absorption. With ∼4 eV of excess energy, geminate recombination takes place on the hundreds of picoseconds time scale, corresponding to thermalization distances ≥40 Å. The recombination of solvated electrons ejected via CTTS detachment of Na−, on the other hand, takes place on two distinct time scales of ≤2 and ∼200 ps with kinetics that cannot be adequately fit by simple diffusive models. The fraction of electrons that undergo the fast recombination process decreases with increasing excitation energy or intensity. These facts lead us to conclude that electrons localize in the vicinity of their geminate Na atom partners, producing either directly overlapping or solvent-separated contact pairs. The distinct recombination kinetics for the two separate electron generation processes serve to emphasize the differences between them: multiphoton ionization produces a delocalized electron whose wave function samples the structure of the equilibrium fluid before undergoing localization, while CTTS is an electron transfer reaction with dynamics controlled by the motions of solvent molecules adjacent to the parent ion. All the results are compared to recent experiments on the photodetachment of electrons in aqueous systems where contact pairs are also thought to be important, allowing us to develop a qualitative picture for the mechanisms of electron generation and recombination in different solvent environments. © 2000 American Institute of Physics.

Notes: Charge-transfer-to-solvent (CTTS) transitions have been the subject of a great deal of interest recently because they represent the simplest possible charge transfer reaction: The CTTS electron transfer from an atomic ion to a cavity in the surrounding solvent involves only electronic degrees of freedom. Most of the work in this area, both experimental and theoretical, has focused on aqueous halides. Experimentally, however, halides make a challenging choice for studying the CTTS phenomenon because the relevant spectroscopic transitions are deep in the UV and because the charge-transfer dynamics can be monitored only indirectly through the appearance of the solvated electron. In this paper, we show that these difficulties can be overcome by taking advantage of the CTTS transitions in solutions of alkali metal anions, in particular, the near-IR CTTS band of sodide (Na−) in tetrahydrofuran (THF). Using femtosecond pump–probe techniques, we have been able to spectroscopically separate and identify transient absorption contributions not only from the solvated electron, but also from the bleaching dynamics of the Na− ground state and from the absorption of the neutral sodium atom. Perhaps most importantly, we also have been able to directly observe the decay of the Na−* excited CTTS state, providing the first direct measure of the electron transfer rate for any CTTS system. Taken together, the data at a variety of pump and probe wavelengths provide a direct test for several kinetic models of the CTTS process. The model which best fits the data assumes a delayed ejection of the electron from the CTTS excited state in ∼700 fs. Once ejected, a fraction of the electrons, which remain localized in the vicinity of the neutral sodium parent atom, recombine on a ∼1.5-ps time scale. The fraction of electrons that recombine depends sensitively on the choice of excitation wavelength, suggesting multiple pathways for charge transfer. The spectrum of the neutral sodium atom, which appears on the ∼700-fs charge-transfer time scale, matches well with a species of stochiometry (Na+, e−) that has been identified in the radiation chemistry literature. All the results are compared to previous studies of both CTTS dynamics and alkali metal solutions, and the implications for charge transfer are discussed. © 2000 American Institute of Physics.

Notes: The organic production technique is a significant innovation for both process and product aspects of the agricultural sector. In less favoured areas, organic production contributes to develop the potential revitalisation of the production sector and also supports the application of endogenous development models, thus favouring sustainable development both on socio-economic and ecological bases. The paper focuses on a case study about the possible growth of organic production in a mountain area of the Florence province, in Tuscany. The organic and non-organic agricultural activities of the area are illustrated, with regards to the whole territorial organisation and the need to maintain agricultural activities for territorial defence. The potential development of the organic product supply is described as a result of a direct survey on the major distribution channels. The main reasons for the delayed expansion of the organic production are outlined in a direct survey on the farms of the area.

Notes: To survive in the global economy small and medium enterprises (SMEs) have to improve their products and processes exploiting their intellectual capital in a dynamic network of knowledge-intensive relations inside and outside their borders. By erasing traditional constraints to SMEs innovation ability and leveraging their flexibility and responsiveness, Information and Communication Technologies (ICT) provide SMEs with opportunities for Knowledge Management (KM) today in most cases largely unexploited. Focusing on the area of Product Innovation (PI) and drawing evidence from the analysis of a multiple-case study on 47 Italian SMEs, patterns in the adoption and use of new ICT tools are explained in relation both to Contingencies and to KM internal processes. Complexity at both product and system levels, emerges as a key factor driving technological choices. Three different KM configurations emerge in relation to ICT approaches. Implications of this study are relevant for both SMEs managers and ICT developers/vendors.

Notes: : The effects of sunflower oil (SFO) and the sucrose esters (SE) P-1670, P-170, and S-170 on crystalline microstructure of a high-melting milk fat fraction (HMF) was studied by polarized-light microscopy (PLM) and confocal laser scanning microsopy (CLSM). The addition of SFO markedly diminished crystal size and delayed crystallization kinetics, as observed in PLM images. Addition of P-1670 modified crystallization behavior only slightly. Addition of P-170 and S-170, however, markedly diminished crystal size and led to more transparent crystals, with lower amount of solids in each crystal. These results show that the microstructural properties of HMF were modifed by addition of SFO and by addition of SPE with low HLB.

Notes: : Crystallization kinetics and rhelogical behavior of blends of high-melting milk-fat fraction (HMF) and sunflower oil (SFO) with and without addition of the sucrose esters P-170, S-170, and P-1670 were investigated. Addition of sucrose esters delayed crystallization, as was evidenced by the longer induction times of crystallization (t) and the lower maximum solid fat content (Smax). Values of penetration force and time corresponding to the 1st peak of curves force compared with time also diminished with addition of SFO. When sucrose esters were added, a solid fat content greater than 10% at the 1st crystallization temperature was necessary to give a stronger structure that could be noticed as higher yield point.