Quantendynamik isolierter molekularer Systeme

The thesis involves three different aspects of quantum dynamics in
cold and isolated molecular systems that are investigated
theoretically with methods ranging from wavepacket dynamics to
density matrix propagation. In the first part the efficiency of
cavity sideband cooling of trapped molecules is theoretically
investigated for the case in which the infrared transition between
two ro-vibrational states is used as a cycling transition. The
molecules are assumed to be trapped either by a radio frequency or
optical trapping potential, depending on whether they are charged
or neutral, and confined inside a high-finesse optical resonator
that enhances radiative emission into the cavity mode. Using
realistic experimental parameters and Carbonyl sulfide as a
molecular representative, we show that in this setup, cooling to
the trap ground state is feasible. The second part investigates
femtosecond pump-probe spectroscopy of single MgH+ ions confined in
an ion trap. The molecular ions are embedded in a coulomb crystal
of atomic magnesium ions which are laser cooled to a few
millikelvin. Single molecules are addressed by femtosecond
ultraviolet laserpulses and the induced molecular processes are
investigated. The simulations of the wave packet motion and
dissociation behavior were used to predict the experimental
parameter regime and are compared directly to the laboratory
results. For this purpose a multiscale model is developed which
involves the wave packet motion as well as the problem of
vibrational heating occurring on a millisecond time scale under
laboratory conditions. The third part investigates the gas phase
SN2 collision reaction of chloride and methyl iodine. Motivated by
the experimental results of Roland Wester and co-workers [Mikosch
et al., Science 319, 183 (2008)], remaining questions were
addressed. The collision reaction is simulated by solving the time
dependent Schrödinger equation on ab initio potential energy
surfaces. With the chosen reactive coordinates it is possible to
reproduce the basic features of the immediate collision reaction.
The internal molecular coordinates are transformed into reaction
path based model which allows for an efficient numerical
description of the nuclear dynamics. The energy transfer in the
system is investigated and compared to the experimental results.
From the new insight into the process, an intuitive concept of a
dynamical barrier can be derived. Moreover the role of the
spectator mode can be clarified.