Photodissociation Dynamics, Quantum Chemistry, Analysis, Control
540 Chemie und zugeordnete Wissenschaften
This work deals with the quantum chemical and quantum dynamical description of
the photodissociation of the transition metal complex cymantrene, CpMn(CO)3
(Cp = Η5-cyclopentadienyl),
by means of ultrashort laser pulses (Femtochemistry). The goal is to understand recent pump-probe and control experiments performed by
Wüste and coworkers (FB Physik, Freie Universität
The Mn-CO bond that dissociates first and ultrafast in experiment
has been chosen as the reaction coordinate.
Within the applied model, this coordinate lies in the plane of symmetry
of the molecule, assuming CS symmetry and a staggered conformation of the
Mn(CO)3 group with respect to the Cp ring.
Quantum chemical ab initio potential energy curves for the lowest-lying neutral
singlet and ionic doublet states are calculated along the reaction
coordinate. The Complete Active Space Self-Consistent Field (CASSCF) method, followed by a Multireference
Contracted Configuration Interaction (MR-CCI) treatment, is
employed. CASSCF and MR-CCI transition dipole moments between neutral
states are computed.
The transition dipole moments coupling the neutral excited
with the ionic states are approximated using the CI coefficients.
In each symmetry, A' and A'', the two lowest excited
i.e. b1A' and c1A', and
a1A'' and b1A'',
avoid crossings in the Franck-Condon region.
The kinetic couplings have been calculated numerically
using the coefficients of the MR-CCI wave function
and their influence on the photodissociation dynamics has been studied
in both the adiabatic
(kinetic coupling) and the diabatic (potential coupling) pictures, which are
equivalent. Simulations of the pump-probe and
control experiments are performed in the adiabatic representation.
It is found that the nonadiabatic coupling between the a1A'' and
the b1A'' states plays a crucial role in the interpretation of
the pump-probe experiments, whereas the b1A' -
c1A' coupling is negligible.
A mechanism explaining the pump-probe experiments for the loss of the first CO ligand
and another which decodes the optimal laser pulse optimizing the parent,
CpMn(CO)3+, ion yield are proposed.
The given analysis can also be extended to predictions about future optimization
experiments yielding predominantly the first daughter ion,
In conclusion, this thesis presents
the first ananlysis of the quantum mechanical details
of an optimal control experiment yielding preferably the target ion,
CpMn(CO)3+, while suppressing competing channels.
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