Evidence of the participation of electronic excited states in the mechanism of positronium formation in substitutional Tb1-xEux(dpm)(3) solid solutions studied by optical and positron annihilation spectroscopies

Positronium formation in the bimary molecular solid solutions Tb1-xEux (dpm)(3) (dpm = dipivaloylmethanate) has been investigated. A strong linear correlation between the D-5(4) Tb(III) energy level excited state lifetime and the positronium formation probability has been observed. This correlation indicates that the ligand-to-metal charge transfer LMCT states act in both luminescence quenching and positronium formation inhibition, as previously proposed. A kinetic mechanism is proposed to explain this correlation and shows that excited electronic states have a very important role in the positronium formation mechanism.CNPqCNPqFAPEMIGFAPEMIGFAPESPFAPESPRENAMI (National Project)RENAMI (National Project

Dialytic transport of carboxylic acids through an anion exchange membrane

The transport behavior of five carboxylic acids of relevance in biotechnology (acetic, propionic, lactic, oxalic, citric) in diffusion dialysis and neutralization dialysis through an anion exchange membrane is investigated. The dependence of acid anion flux on base concentration in neutralization dialysis is analyzed in terms of two limiting situations (boundary layer control and membrane control) by an empirical two-parameter flux equation in formal analogy to a Langmuir function. When coupled to a life fermenter, neutralization dialysis is a means to control the pH of the fermentation medium. By removing biotoxic acids, it improves microbial productivity, as exemplified with the Propioni system producing vitamin B_1_2 and propionic acid. (orig.)Also published in Journal of Membrane Science, vol. 139 (1998), p. 137-143Available from TIB Hannover: RA 3251(98/E/31) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman