https://doi.org/10.1007/s100530170077
Theoretical exploration of ultrafast spectroscopy of small clusters
1
Walther-Nernst-Institut für Physikalische und Theoretische Chemie, Humboldt-Universität zu Berlin,
Bunsenstraße 1, 10117 Berlin, Germany
2
J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova
3, CZ-18223 Prague
Corresponding author: a vbk@chemie.hu-berlin.de
Received:
22
December
2000
Published online: 15 September 2001
We present the ultrafast multistate nuclear dynamics involving adiabatic and
nonadiabatic excited states of non-stoichiometric halide deficient clusters
(NanF
) characterized by strong ionic bonding and one-excess electron
for which the "frozen ionic bonds" approximation has been justified allowing to
consider the optical response of the single excess electron in the effective field of
the other electrons. We combined the Wigner-Moyal representation of the
vibronic density matrix with the ab initio multi state molecular dynamics in
the ground and excited electronic states including the nonadiabatic couplings
calculated "on the fly" at low computational demand.
This method allows the simulation of femtosecond pump-probe and pump-dump signals
based on an analytical formulation, which utilizes temperature dependent ground
state initial conditions, an ensemble of trajectories carried out on the electronic
excited state as well as on the ground state after the passage through the conical
intersection in the case of nonadiabatic dynamics and for probing either in the
cationic state or in the ground state. The choice of the systems we presented
has been made in order to determine the timescales of the fast
geometric relaxation leaving the bonding frame intact as during the dynamics
in the first excited state of Na4F3, and of the bond breaking processes leading to
conical intersection between the first excited state and the ground state as
in Na3F2. The former is the smallest finite system prototype
for an surface F-center of bulk color centers. The latter allows to study the photo
isomerization in full complexity taking into account all degrees of freedom.
In the case of Na4F3 after the fast geometric
relaxation in the excited state leading to deformed cuboidal structure
without breaking of bonds, different types of internal vibrational redistribution
(IVR) processes have been identified in pump-dump signals by tuning the dump laser.
In contrast,
from the analysis of the pump-probe signals of Na3F2
cluster, the timescales for the metallic and the
ionic bond breaking, as well as for the passage through conical
intersection have been determined. Finally the
conditions under which these processes can be experimentally observed have been
identified.
PACS: 31.15.Qg – Molecular dynamics and other numerical methods / 71.15.Qe – Excited states: methodology
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001
