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Ultrafast electron dynamics in the low-femtosecond regime was evaluated for poly(thiophene) by resonant Auger spectroscopy using the corehole clock method. Sulfur KL 2,3 L 2,3 Auger decay spectra were measured as a function of the photon energy. Remarkable changes developed by tuning the photon energy along the sulfur 1s absorption edge, depending on the nature of the intermediate core excited states. Features characteristics of the Auger Resonant Raman effect were observed. Competition between core hole decay and delocalization of the photoexcited electron was monitored. Branching ratios of Raman (spectator) and normal Auger channels were calculated and electron delocalization times derived.

ABSTRACT:The semiempirical AM1 and PM3 methods, as well as the density functional (DFT/B3LYP) approach using the 6-31g(d) basis set, were employed to calculate the relative stability of intermediate radicals derived from artemisinin, a sesquiterpene lactone having an endoperoxide bridge that is essential for its antimalarial activity. The compounds studied have their nonperoxidic oxygen atom of the trioxane ring and/or the carbonyl group replaced by a CH 2 unit. Relative stabilities were calculated by means of isodesmic equations using artemisinin as reference. It was found that replacement of oxygen atoms decreases the relative stability of the anionic radical intermediates. In contrast, for compounds with inverted stereochemistry the intermediate radicals were found to be more stable than those with the artemisinin-like stereochemistry. These relative stabilities may modulate the antimalarial potency. Radicals centered on carbon are always more stable than the corresponding radicals centered on oxygen.

Methanol and ethanol, precursors of prebiotic molecules, are found in interstellar and circumstellar environments. At low temperatures, electrons may interact with these frozen molecules on dust grain surfaces stimulating desorption of atomic and molecular ions and charged clusters. These heavy fragments released from the icy mantles could contribute to the abundance in the gas phase of organic molecules in such environments. In this work, we investigate the ionic fragments desorbed from methanol and ethanol pure ices due to high energy electron impact. Absolute desorption yields (ions/impact) for each fragment desorbed from the ice surface were determined. Several clusters and heavier molecular ions were observed at higher electron energies. Two mechanisms seem to be involved in the desorption process, namely, the Auger stimulated ion desorption and that of secondary electrons. These data may provide support to establish more accurate astrochemical models and contribute to explain the influence of solar wind on condensed alcohols.

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