The thesis is a summary and discussion of eight papers. During the last decades, precipitation has become increasingly acidic due to the extensive use of fossil fuels. In areas of poorly buffered bedrocks, e.g. Scandinavia, northeastern United States, this phenomenon has resulted in elevated amounts of Al(III) being leached into streams and lakes. Recent findings reveal that these elevated Al-concentrations could cause fish death and decreasing forest production. In the present thesis, the importance of taking naturally occurring substances into consideration when discussing Al(III) in natural waters, is emphasized. On the basis of a chemical characterization of relevant ligand classes in a natural water, the complex formation between Al^+, hydroxide ions and the inorganic ligand carbonic acid, the low-molecular weight organic ligand citric acid and the high-molecular weight model substances gallic acid, 1,2-dihydroxynaphtha-lene-4-sulfonate, 1,2-naphthoquinone-4-sulfonate, pyrocatechol and salicylic acid were investigated. The investigations were performed as series of Potentiometrie titrations and data were processed by means of the least-squares computer program LETAGROPVRID using a technique called pqr-analysis, permitting an unbiased search for complex model (and corresponding equilibrium constants) to be made. In most systems studied, the complexation at high ligand excesses can be described by a series of mononuclear complexes AIL-AIL^. Tentatively, the whole series consists of octahedrally coordinated (water and ligand oxygens) AI(III). At lower ligand excesses, the significance and in some cases even predominance of ternary mono- and polynuclear hydroxo complexes is demonstrated. In two of the systems, binary aluminium hydroxo species are evaluated. The potential importance of the substances with respect to Al-com-plexation in natural waters are indicated in a number of model calculations. The solubility of the clay mineral kaolinite is calculated as a function of -lg[H+] and ligand concentration. It is shown that citric acid, gallic acid, 1,2-dihydroxynaphthalene-4-sulfonate, pyrocatechol and salicylic acid contribute quite significant to the total solubilities, even at very low concentrations. As a complement and background to the equilibrium studies, the corrosion rate for one of the naturally occurring Al-bearing minerals, corundum, is reported. In this investigation, performed with a leach-ant solution of ground-water composition, an experimental technique was employed which made it possible to divide the corrosion into chemical and mechanical losses. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1983</p> / digitalisering@umu

Die Reaktionspfade und Reaktionsdynamik photoinduzierter bimolekularer Ladungstransferreaktionen werden mit Hilfe der ultraschnellen polarisationsabhängigen UV-Pump/IR-Probe-Spektroskopie charakterisiert. Allgemein akzeptierte Modelle zur Beschreibung von bimolekularen Elektrontranserreaktionen nehmen an, dass Ladungstrennung in polaren Lösungsmitteln zu zwei Arten von Ionenpaaren führt, den lockeren (LIPs) und den engen Ionenpaaren (TIPs). TIPs und LIPs können durch die Beobachtung von Schwingungsmoden spektroskopisch unterschieden werden. Allerdings deuten die multiplen Zeitskalen sowohl für die Bildung von TIPs als auch LIPs darauf hin, dass eine Unterscheidung in zwei Arten von Ionenpaaren mit definierter Geometrie eine erhebliche Vereinfachung ist. TIPs und LIPs sind vielmehr als Grenzfälle zu betrachten, zwischen derer eine kontinuierliche Verteilung verschiedener Ionenpaare existiert. Die Natur der Ionenpaare wird durch die Verteilung der neutralen Reaktionspaare vor Initiation der Reaktion bestimmt. Außerdem wird gezeigt, dass TIPs höchst anisotrop sind. Die Wichtigkeit der beidseitigen Orientierung der Reaktanten wird dabei offengelegt. Weiterhin wird erstmalig ein femtosekundenspektroskopischer Beweis für die Existenz von Kohlensäure in wäßriger Lösung präsentiert. Eine Photosäure wurde verwendet, um die ultraschnelle Protonierung von Bikarbonat optisch auszulösen. Kohlensäure wurde bisher als Feststoff in Eismatrizen und in der Gasphase detektiert. Da Kohlensäure als Intermediat zwischen Kohlenstoffdioxid und Bikarbonat postuliert wird, ist ihre Charakterisierung von immenser Bedeutung für das Verständnis grundlegender Säure-Base Chemie von Karbonaten in wäßriger Lösung. Die Analyse der zeitabhängigen Signale unter Verwendung eines theoretischen Modells erlaubt die Bestimmung der bimolekularen Reaktionsdynamik. Dies ermöglicht einen Einblick in die Säure-Base Chemie von Kohlensäure. / The reaction pathways and dynamics of photoinduced bimolecular charge transfer reactions are characterised with ultrafast polarisation-sensitive UV-pump/IR-probe-spectroscopy. Generally accepted models for bimolecular electron transfer reactions suppose that charge separation in polar solvents leads to two geminate ion pairs, namely loose (LIPs) and tight ion pairs (TIPs). By monitoring vibrational marker modes TIPs and LIPs can be distinguished spectroscopically. However, multiple time scales for the formation of TIPs and LIPs indicate that a distinction between two kinds of ion pairs with well-defined geometries is a considerable simplification. TIPs and LIPs should rather be regarded as limiting cases, as there is a continuous distribution of different ion pairs between these two limits. The crucial parameter governing the nature of the ion pairs is the distribution of neutral reaction pairs subsequent to initiation of the reaction. Furthermore, TIPs are found to be highly anisotropic, revealing the importance of mutual orientation of the reactants. This thesis also presents for the first time femtosecond infrared spectroscopic results proving the existence of carbonic acid in aqueous solution. A photoacid is used to optically trigger the ultrafast protonation of bicarbonate. Carbonic acid has only been detected as solid existing in ice matrices and in the gas phase, so far. Because carbonic acid is often postulated as intermediate between carbon dioxide and bicarbonate its characterisation is of substantial support in understanding fundamental acid-base chemistry of carbonates in aqueous solution as well as in biophysical situations. Analysing the time-dependent signals using a theoretical model to describe bimolecular reaction dynamics an on-contact proton transfer reaction rate is derived. This gives an insight into the acid-base chemistry of carbonic acid.

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