Singlet versus triplet dynamics of β-carotene studied by quantum control spectroscopy

Biomolecules very often present complex energy deactivation networks with overlapping electronic absorption bands, making their study a difficult task. This can be especially true in transient absorption spectroscopy when signals from bleach, excited state absorption and stimulated emission contribute to the signal. However, quantum control spectroscopy can be used to discriminate specific electronic states of interest by applying specifically designed laser pulses. Recently, we have shown the control of energy flow in bacterial light-harvesting using shaped pump pulses in the visible and the selective population of pathways in carotenoids using an additional depletion pulse in the transient absorption technique. Here, we apply a closed-loop optimization approach to β-carotene using a spatial light modulator to decipher the energy flow network after a multiphoton excitation with a shaped ultrashort pulse in the near-IR. After excitation, two overlapping bands were detected and identified as the S₁ state and the first triplet state T₁. Using the transient absorption signal at a specific probe delay as feedback, the triplet signal could be optimized over the singlet contribution.     

Profinite groups of finite cohomological dimension

Let 1→N→G→G/N→1 be a short exact sequence of profinite groups, and let p be a prime number. We prove that if G is of finite cohomological p-dimension n:=cd_p(G)<∞ and if the order of $\text{H}{}^{\mathrm{k}}\text{(N,}\text{F}{}_{\mathrm{p}}\text{)}$ is finite for k:=cd_p(N), the virtual cohomological p-dimension of G/N equals n?k. To cite this article: T. Weigel, P. Zalesskii, C. R. Acad. Sci. Paris, Ser. I 338 (2004).     

R?ntgenspektroskopie

Ohne Zusammenfassung     

Die gravimetrische Phosphorbestimmung in wolframhaltigen St?hlen

Zusammenfassung Einige der üblichen Methoden zur Phosphorbestimmung in wolframlegierten Stählen werden unter Anwendung von ¹⁸⁵W und ³²P einer Nachprüfung unterzogen. Dabei erweisen sich die Phosphorverluste durch Adsorption an dem Wolframsäureniederschlag als gering, so daß sie bei weniger anspruchsvollen Bestimmungen unberücksichtigt bleiben können. Erheblich größer sind dagegen die Fehler, die durch Mitfällung von Wolframsäure mit dem Ammoniummolybdatophosphatniederschlag entstehen können. Es werden zwei Methoden angegeben, nach denen eine quantitative Abtrennung des Wolframs und damit eine sichere Bestimmung des Phosphors möglich ist.Herr Prof. Dr.-Ing. K. Schwabe ermöglichte es uns freundlicherweise, die Untersuchungen mit radioaktivem Wolfram und Phosphor im Zentralinstitut für Kernphysik Rossendorf, Bereich Radiochemie, durchzuführen. Ihm sei auch an dieser Stelle herzlichst gedankt.     

Computer assisted multielement analysis of terrestrial and extraterrestrial materials and studies on long-lived cosmogenic53Mn by neutron activation

In a large number of alpine rocks and respective mineral separates the beryllium distribution was studied via “non-destructive” photon activation. The detection limit of the assembly was ∼20 ppb. The existence of Be-rich areas was revealed. A selection of individual rocks was analysed by instrumental as well as by radiochemical neutron activation analysis for main and trace elements as: Na, K, Sc, Cr, Mn, Fe, Co, Rb, Cs, La, Eu, Yb, Ta, W, Au, and U. The latter was determined by counting the²³⁵U-fission tracks. The data supply an insight into the complex processes leading to the formation of metamorphic rocks. The hardware and the computer evaluation of the γ-spectra is described in some detail. A further application is the determination of traces of⁵³Mn (in the order of 10⁻¹² g/g) produced by the interaction of cosmic rays with stony meteorites. From a comparison of the²⁶Al- and⁵³Mn-values it is concluded that the depth dependent production of these two radionuclides differs slightly.