The S-1/S-2 exciton interaction in 2-pyridone center dot 6-methyl-2-pyridone: Davydov splitting, vibronic coupling, and vibronic quenching

The excitonic splitting between the S-1 and S-2 electronic states of the doubly hydrogen-bonded dimer 2-pyridone center dot 6-methyl-2-pyridone (2PY center dot 6M2PY) is studied in a supersonic jet, applying two-color resonant two-photon ionization (2C-R2PI), UV-UV depletion, and dispersed fluorescence spectroscopies. In contrast to the C-2h symmetric (2-pyridone) 2 homodimer, in which the S-1 <- S-0 transition is symmetry-forbidden but the S-2 <- S-0 transition is allowed, the symmetry-breaking by the additional methyl group in 2PY center dot 6M2PY leads to the appearance of both the S-1 and S-2 origins, which are separated by Delta(exp) = 154 cm(-1). When combined with the separation of the S-1 <- S-0 excitations of 6M2PY and 2PY, which is delta = 102 cm(-1), one obtains an S-1/S-2 exciton coupling matrix element of V-AB, el = 57 cm(-1) in a Frenkel-Davydov exciton model. The vibronic couplings in the S-1/S-2 <- S-0 spectrum of 2PY center dot 6M2PY are treated by the Fulton-Gouterman single-mode model. We consider independent couplings to the intramolecular 6a' vibration and to the intermolecular sigma' stretch, and obtain a semi-quantitative fit to the observed spectrum. The dimensionless excitonic couplings are C(6a') = 0.15 and C(sigma') = 0.05, which places this dimer in the weak-coupling limit. However, the S-1/S-2 state exciton splittings Delta(calc) calculated by the configuration interaction singles method (CIS), time-dependent Hartree-Fock (TD-HF), and approximate second-order coupled-cluster method (CC2) are between 1100 and 1450 cm(-1), or seven to nine times larger than observed. These huge errors result from the neglect of the coupling to the optically active intra-and intermolecular vibrations of the dimer, which lead to vibronic quenching of the purely electronic excitonic splitting. For 2PY center dot 6M2PY the electronic splitting is quenched by a factor of similar to 30 (i.e., the vibronic quenching factor is Gamma(exp) = 0.035), which brings the calculated splittings into close agreement with the experimentally observed value. The 2C-R2PI and fluorescence spectra of the tautomeric species 2-hydroxypyridine center dot 6-methyl-2-pyridone (2HP center dot 6M2PY) are also observed and assigned. (C) 2011 American Institute of Physics.

Ästhetische Meerfahrt. Erkundungen zur Beziehung zwischen Literatur und Natur in der Neuzeit

Die Beziehungen zwischen Mensch und Natur durchziehen sämtliche Christian von Zimmermann Kulturräume und werden in den verschiedensten kulturellen Praktiken gestaltet. Dies gilt besonders auch für die Literatur. Sprachliches und besonders auch ästhetisch gestaltetes sprachliches Handeln wird getragen von historisch sich wandelnden Einstellungen zum Meer (Mentalitätsgeschichte), prägt die Beziehung zwischen Mensch und Naturraum (literarische Anthropologie) und kulminiert in der Anforderung an eine ‘rechte Rede’ im Umgang mit der Natur (Naturethik). Unter dem Titel Ästhetische Meerfahrt werden Schlaglichter auf diese Aspekte der Geschichte der Mensch-Meer- Beziehungen im Medium der Literatur geworfen. Dabei stellt die Studie selbst eine Meerfahrt (Essay) dar, die Land- und Seemarken benennt, einzelne Häfen ansteuert, sich aber der offenen Weite des Gewässers bewusst bleibt. Eigene Erkundungen anzuregen, ein naturethisches Denken in die Literaturwissenschaft einzubeziehen, ist Anliegen dieses Buches. Wichtige, teils ausführlich dargelegte Stationen des Buches sind Werke von Olearius, Fleming, Brockes, Gessner, Herder, Goethe, Kosegarten, Heine, Ibsen, Storm, Hauptmann, Keyserling, Kellermann, Fock, Andersch, Cibulka, Theobaldy.