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leads to photoelectron distributions which vary with the delay between a
pump– and a probe–pulse. If the vibrational wave packet as prepared in
the pump–transition is located in a region where the bonding character
is ionic, the photoelectron, due to its localization on the iodine atom,
may be ejected directly or be scattered from the Na + ion. This leads to
structures in the photoelectron spectrum which, in turn, reflect temporal
bond-length changes.
MO 12.12 Di 14:00 Schellingstr. 3
Photoinduzierte Prozesse in biologischen Systemen —
•Benjamin Dietzek 1 , Raman Maksimenka 1 , Gudrun Hermann
2 , Wolfgang Kiefer 1 , Jürgen Popp 3 und Michael
Schmitt 1,3 — 1 Institut für Physikalische Chemie, Universität
Würzburg, Am Hubland, 97074 Würzburg — 2 Institut für Biochemie
und Biophysik, Universität Jena, Philosophenweg 12, 07743 Jena —
3 Institut für Physikalische Chemie, Universität Jena, Helholtzweg 4,
07743 Jena
Licht-induzierte Prozesse in biologisch relevanten Systemen zeichnen
sich durch die hohe Effizienz des biologisch vorteilhaften Prozesses gegenüber
dissipativen Konkurrenzprozessen aus. Für das Verständnis von
Prozessen in biologischen Systemen ist es somit notwendig, die Voraussetzungen
für diese hohe Selektivität zu charakterisieren. Für die Beschreibung
solcher biologisch relevanter Systeme wie zum Beispiel Phytochrom
oder Protochlorophyllid A ist eine Untersuchung der unmittelbar
auf die Lichtabsorption folgenden, ultraschnell ablaufenden strahlungslosen
Deaktivierungsprozessen notwendig. Die Charakterisierung dieser
Primärprozesse wurde mittels fs-zeitaufgelöster transienter Absorption
und der transienten Gitter-Spektroskopie mit einer Zeitauflösung
von 80 fs vorgenommen. Im Falle von Phycocyanobilin, einem Modellchromophor
für das Enzym Phytochrom wurde eine starke Pumpwellenlängenabhängigkeit
der Fotoreaktionszeit beobachtet. Die experimentellen
Daten bestätigen ein kinetisches Modell für die lichtinduzierten
Prozesse in Phycocyanobilin.
MO 12.13 Di 14:00 Schellingstr. 3
The investigation of excited-state dynamics of polyatomic
molecules by means of fs time-resolved four-wave mixing
spectroscopy — •Maksimenka Raman 1 , Benjamin Dietzek 1 ,
Torsten Siebert 1 , Wolfgang Kiefer 1 , and Michael Schmitt 1,2
— 1 Institut für Physikalische Chemie, Universität Würzburg, Am
Hubland, 97074, Würzburg — 2 Institut für Physikalische Chemie,
Universität Jena, Helmholtzweg 4, 07743 Jena
The evolution of molecules in their excited states is of great interest in
physics, chemistry and biology, since the absoption of a photon may e.g.
lead to photoreactions. Therefore it is important to explore the relaxation
pathways of molecules after photoexcitation. Especially the roles of certain
nuclear degrees of freedom invloved in radiationless transitions need
to be elucidated. We demonstrate that different fs time-resolved fourwave
mixing schemes can be applied to investigate the excited-state dynamics
of polyatomic molecules. Thus coherent anti-Stokes Raman scattering
(CARS) is capable to selectively interrogate the role of specific
Raman modes. This technique has been applied to directly observe the
redistribution of vibrational energy between different modes of Stilbene
3 taking place after photoexcitation. Time-resolved CARS was used to
identify shifts of normal modes positions in the excited state in comparison
to the ground state. Furthermore, transient grating spectroscopy was
used to characterize radiationless transitions between various electronic
states in azulene derivatives. In summary, different fs four-wave mixing
schemes were successfully applied to characterize dynamical processes in
polyatomic molecules induced by photoexcitation.
MO 12.14 Di 14:00 Schellingstr. 3
FS-Study on Carotenoid to Bacteriochlorophyll Energy-
Transfer in Light-Harvesting1 Complexes from Rhodospirillum
rubrum with Carotenoids of Different Conjugation Lengths —
•Peter Gaertner 1 , Helmut Port 1 , Markus Branschaedel 2
und Robin ghosh 2 — 1 3. Physikalisches Institut — 2 Department of
Bioenergetics, Institute of Biology, Uni Stuttgart
This contribution comprises a comparative fs-spectroscopic study on
light-harvesting complexes 1 (LH1) from mutants of Rhodospirillum rubrum
(R.r.). These complexes contain carotenoids (Car) of different conjugation
lengths (n=13 or n=11, resp.), but no reaction center. After
selective excitation of different electronic states of the pigments and comparison
with the LH1 of a carotenoid-less mutant, we are able to draw
conclusions about Car to Bacteriochlorophyll (BChl) energy-transfer.
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MO 12.15 Di 14:00 Schellingstr. 3
Ultrafast Infrared Spectroscopy on Ground State Dynamics
during Photoisomerisations — •Florian Koller, Tobias
Schrader, Wolfgang Schreier, Arne Sieg, Wolfgang Zinth,
and Peter Gilch — Sektion Physik, Ludwig-Maximilians-Universität,
Oettingenstr. 67, D-80538 München, Germany
Photoisomerisations are often accompanied by a rapid (100 fs – 1 ps)
depletion of the excited state. These dynamics can be studied by femtosecond
fluorescence and absorption spectroscopy. Little is known on the
ensuing processes in the electronic ground state. Time resolved IR spectroscopy
can open the route to a detailed understanding of the structural
re-arrangements and the vibrational relaxation in the ground state. This
is demonstrated by IR experiments (in the range of 1520 – 1050 cm −1
) on the isomerisation of 4 − nitro − 4 ′ (dimethylamino) − azobenzene
(NA). The decay of the excited state was followed by the disappearance
of an IR line at 1275 cm −1 reproducing the fluorescence decay time. At
later stages, apart from cooling processes on the 5 ps time scale, surprisingly
slow dynamics (up to 200 ps) due to structural re-arrangements are
detected.
MO 12.16 Di 14:00 Schellingstr. 3
An RF trap for anion-molecule reaction dynamics — •Jochen
Mikosch 1,2 , Dirk Schwalm 2 , Matthias Weidemüller 1 , and
Roland Wester 1 — 1 Physikalisches Insitut, Universität Freiburg,
79104 Freiburg — 2 Max-Planck-Institut für Kernphysik, 69117
Heidelberg
We have set up a cold negative ion cluster source and an RF ion trap
to investigate anion-molecule reactions in a controlled experiment that
allows us to prepare negative molecular ions and clusters with controlled
internal and translational excitation. Anion-molecule reactions are important
in various environments, from the liquid phase to the Earth’s
atmosphere. For selected reaction systems total and differential cross
section measurements will be performed. Furthermore, reactions inside
water clusters will be investigated which offer a controlled microscopic
view on dynamics at the transition from the gaseous to the liquid phase.
MO 12.17 Di 14:00 Schellingstr. 3
Unimolecular fragmentation of anthracene and phenanthrene —
•Adalbert Ding, Christian Lenski, and Michael Lenski — Technische
Universität Berlin, Optisches Institut, Sekr. P1–1, Strasse des 17.
Juni 135, D–10623 Berlin
Most favoured theories concerning the diffuse interstellar bands propose
that the observed radiation originates from infrared fluorescences of
vibronic highly excited polycyclic aromatic hydrocarbons. In the present
study light from the Berlin synchrotron BESSY was used to investigate
the fragmentation of anthracene and phenanthrene.
By evaporation of the solid substances in an oven an effusive beam of
target molecules was produced. After having been ionized using photon
energies between 10 eV and 30 eV the fragmentation of these substances
was analysed by means of time–of–flight–mass–spectrometry.
Comparison of experimental results with RRKM–calculations serves
to clarify if anthracene and phenanthrene isomerize to identical intermediate
states prior to fragmentation.
MO 12.18 Di 14:00 Schellingstr. 3
Vollständige Bestimmung der Geschwindigkeitsvektoren einzelner
Photodissoziationsfragmente mittels 3D-Imaging — •Niels
Gödecke, Karl-Heinz Gericke, Christof Maul und Oliver Ott
— Institut für Physikalische Chemie, TU Braunschweig, D-38106 Braunschweig
Zur vollständigen Charakterisierung unimolekularer laserinduzierter
Photodissoziationsprozesse gehören neben der Kenntnis der beteiligten
Energiezustände ebenso Informationen über die räumliche Verteilung
der Reaktionsprodukte. Um die gewünschten Größen direkt, d.h. ohne
den Einsatz fehlerbehafteter Inversionsalgorithmen, ermitteln zu können,
wurde eine Apparatur entwickelt, die es erlaubt, die entstehenden Fragmente
orts-, zeit- und zustandsaufgelöst zu detektieren. Ermöglicht
wird dies durch die Kombination von Molekularstrahl, Flugzeit-
Massenspektrometrie, resonanz-verstärkter Multiphotonenionisation und
einer Delay-Line-Anode als Detektor. Die Technik wird am Beispiel der
Photodissoziation von Thiophosgen (CSCl2) bei einer Wellenlänge von
235 nm vorgestellt. Neben dem Verzweigungsverhältnis und der Verteilung
der kinetischen Energie für Chlor im Grundzustand Cl und Spin-
Bahn-angeregtem Chlor Cl ∗ sowie der CSCl-Partnerfragmentverteilung