aktualisiertes pdf - DPG-Tagungen

The effect of optical pumping on the Autler-Townes splitting in a cascade
scheme X 1 Σ + g → A 1 Σ + u → 5 1 Σ + g in Na 2 molecules has been studied
with high resolution using a well collimated supersonic molecular beam.
The initially populated lower level is coupled by a strong cw laser field
with the intermediate level. The intermediate level is probed by a weak
cw laser field at frequencies around the resonance with the upper level.
Depending on the detuning of the coupling laser, the excitation spectrum
of the upper level shows either only one narrow peak, or a strongly
distorted double peak structure, or one broad asymmetric peak. This observation
is explained by interplay between optical pumping and ac Stark
shift. Improper interpretations of earlier studies of Autler-Townes effect
in similar schemes are also discussed.
MO 17.15 Do 14:00 Schellingstr. 3
Stark-Effekt des asymmetrischen Rotators - das Programm
STARS — •Elke Heinecke, Markus Glugla und Achim Hese
— Technische Universität Berlin, Institut für Atomare Physik und Fachdidaktik
Wir stellen das von uns entwickelte Programm STARS zur Berechnung
des Stark-Effektes des asymmetrischen Rotators vor. Das Programm berechnet
den Stark-Effekt des asymmetrischen Rotators wahlweise durch
Diagonalisierung der Stark-Matrix oder via Störungsrechnung. Es erlaubt
sowohl die Simulation ganzer Stark-Spektren als auch die Berechnung einzelner
Linienaufspaltungen und -verschiebungen auf der Basis von Dipolmomenten
und Polarisierbarkeiten. Das Programm läuft unter Windows
und ist einfach zu bedienen.
MO 17.16 Do 14:00 Schellingstr. 3
Use of point–group symmetries in the analysis of vibrational
spectra — •Katya Rykhlinskaya and Stephan Fritzsche — Universität
Kassel, Institut für Physik, D–34132 Kassel, Germany
In recent years, a large number of experiments has been carried out
to study the properties of molecules and clusters. They often use the
techniques of vibrational spectroscopy to resolve the geometrical structure
and the bonds of the molecules. Two experimental techniques are
known today to measure the vibrational spectra of the molecules: infrared
absorption and Raman scattering [1]. However, in order to derive
the symmetry and structure of the molecules from the observed spectra,
they have to be combined with point group theory. To facilitate the use
of this theory in vibrational spectroscopy, here we present and discuss a
set of Maple procedures (called the Bethe package [2]). We show in
particular how these procedures can be used to analyse the spectra from
infrared and Raman spectroscopy. In addition, the interactive design of
this package may help the user in following up the literature and in daily
research work.
[1] D. C. Harris, M. D. Bertolucci, Symmetry and Spectroscopy (Dover
Publication, New York, 1989).
[2] S. Fritzsche and K. Rykhlinskaya, Comp. Phys. Commun., submitted
(2003).
MO 17.17 Do 14:00 Schellingstr. 3
Spektroskopische Charakterisierung von (protonierten) Imidazol
Clusterionen — •Nicola Solca, Horia-Sorin Andrei und Otto
Dopfer — Physikalische Chemie, Universität Würzburg, Am Hubland,
97074 Würzburg
Imidazol (Im=C3N2H4) ist ein heterozyklischer, stark basischer aromatischer
Fünfring von zentraler Bedeutung in der Biochemie, da Im
ein Baustein der beiden DNA Basen Adenin und Guanin darstellt. Zudem
werden H-brückengebundene Ketten der Form Imm als aussichtsreiche
Kandidaten für effektive Protonenleiter in modernen Brennstoffzellen
diskutiert. Daher sind Studien zu den geladenen bzw. protonierten Imidazolketten
und deren Solvatationsverhalten von grundlegendem Interesse.
In diesem Beitrag berichten wir über die spektroskopische Charakterisierung
von Clustern der Form Im + -Ln und ImmH + -Ln mit Hilfe der IR
Photodissoziation [1]. Dabei stehen folgende Fragestellungen im Vordergrund:
(1) Im und ImH + bieten mehrere attraktive Bindungsplätze für
neutrale Liganden L an (z.B. H-Brücken bzw. π-Bindungen), deren Bindungsstärke
vom Grad der Protonierung und der Anzahl der Im Einheiten
(m) im Cluster abhängt; (2) die Azidität der N-H Bindungen in ImmH + -
Ln hängt ebenfalls von der Kettenlänge m und der Art und Anzahl der
Liganden ab. Die Analyse der IR Spektren führt im Zusammenspiel mit
quantenchemischen Methoden zu einem detaillierten Verständnis dieser
elementaren Phänomene auf molekularer Ebene.
[1] O. Dopfer, Int. Rev. Phys. Chem. 22, 437 (2003).
MO 17.18 Do 14:00 Schellingstr. 3
Infrared spectroscopy of gas phase cluster anions — •J. Mathias
Weber, Holger Schneider, and Alexia Glöß — Institut
für Physikalische Chemie, Universität Karlsruhe, D-76128 Karlsruhe,
Deutschland
Ion-molecule complexes of atomic anions with carbon dioxide have
been studied by gas phase infrared photodissociation spectroscopy. Ions
were formed by attachment of secondary electrons to atomic and molecular
precursors in the electron impact plasma generated in the high density
region of a pulsed supersonic expansion. Ions were mass selected using
a time-of-flight mass spectrometer, and interacted with pulsed infrared
radiation from an optical parametric oscillator/amplifier. Spectra were
taken between 2250 cm −1 and 3800 cm −1 by monitoring the fragment
ions generated by vibrational predissociation, and interpreted using quantum
chemical calculations. We observe that for clusters containing halide
anions, the asymmetric stretch mode of the carbon dioxide molecule is
red shifted from the frequency of free carbon dioxide, with the red shift
increasing towards the lighter halide ions.
MO 17.19 Do 14:00 Schellingstr. 3
Photoelectron Spectroscopy of Isolated Multiply Charged
Oligonucleotides — •J. Mathias Weber 1 , Ilya N. Ioffe 2 , Katja
M. Berndt 1 , Daniel Löffler 1 , Jochen Friedrich 1 , Oli T.
Ehrler 1 , Joel H. Parks 3 , and Manfred M. Kappes 1 — 1 Institut
für Physikalische Chemie, Universität Karlsruhe, D-76128 Karlsruhe,
Germany — 2 Chemistry Department, Moscow State University, Moscow
119899, Russia — 3 The Rowland Institute at Harvard, 100 Edwin H.
Land Boulevard, Cambridge, MA 02142, USA
Mass spectrometry and ultraviolet photoelectron spectroscopy were
used to investigate the electronic properties of isolated DNA oligonucleotides.
[dA5 − 4H] 4− , and [dT5 − 4H] 4− ions carrying four negative
charges were formed by electrospray ionization and mass selected in
an ion beam. Their photoelectron spectra were analyzed using a magnetic
bottle electron spectrometer. We find the fourth electron affinity
to be slightly negative (-0.30(15) eV) for [dA5 − 4H], while it is positive
(+0.90(15) eV) for [dT5 − 4H]. This significant influence of the base composition
on energetics is in turn relevant for analytic applications as well
as in the context of DNA charge transfer properties.
MO 17.20 Do 14:00 Schellingstr. 3
Characterization of a carbon sublimation source for studying
the growth of small carbon cluster ions C + n . — •Silvio Decker,
Igor Savić, Ivo Čermák, and Dieter Gerlich — Department of
Physics, Technische Universität Chemnitz, 09126 Chemnitz, Germany
For studying astrochemically relevant collision processes between
stored ions (e.g. C + n or D+ 3 ) and carbon atoms and molecules, a sublimation
source has been integrated into an ion trapping apparatus. The
sublimation efficiency of two permanently compressed and electrically
heated carbon rods has been characterized as a function of the heating
power and the resulting operating temperature. The flux of the emitted
C, C2 und C3 molecules has been determined via two different methods,
electron bombardment and deuteron transfer reactions by analyzing the
trap content with a mass spectrometer. Assuming a translational temperature
of 3000 K one obtains in the trap which is at a distance of 40 cm, a
carbon number density of up to 10 8 cm −3 . A detailed analysis has shown,
that a large fraction of the emitted carbon (>70%) condenses already on
the rods or in close vicinity. Quantitative analysis of the increase of C + 4
product ions allows us to conclude that these ions are growing with rate
coefficients larger than 10 −11 cm 3 s −1 .
MO 17.21 Do 14:00 Schellingstr. 3
Study of H + 3 production and rotational de-excitation in a
hollow cathode ion source — •Simon M. Altevogt 1 , Henrik B.
Pedersen 1 , Vola Andrianarijaona 1 , Henrik Buhr 1 , Holger
Kreckel 1 , Sven Krohn 1 , Lutz Lammich 1 , Daniel Strasser 2 ,
Daniel Zajfman 2 , Dirk Schwalm 1 , and Andreas Wolf 1 —
1 Max-Planck-Institut für Kernphysik, 69117 Heidelberg, Germany —
2 Weizman Institut of Science, 76100 Rehovot, Israel
In many plasma ion sources H + 3 is produced with high rovibrational
excitation (3000K). With the aim of producing rotationally cold H + 3 ions
a hollow cathode ion source has been built closely following a design in
use in the group of Prof. H. Helm at the Universität Freiburg. The liquid
nitrogen cooled source delivers a stable current of up to several µA of
H + 3 . Detailed dependencies of the ion yield on the inside H2-gas pressure,
discharge intensity and electrical extraction field strength in the ion drift
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