| Details: |
Electron or photon-induced ionization and fragmentation processes of molecular ions
are fundamental reactions in many scientific research fields ranging from molecular
physics to astrophysics and medical applications. Detailed studies of the reaction
products and their dynamics lead to a deeper understanding of the underlying molecular
structure. Typical observables of the structural characteristics are the fine splitting of
energy levels, population of excited states, and lifetimes of metastable states. Depending
on the energy of the collision process, several reaction channels such as direct
ionization, fragmentation, evaporation (loss of H, H 2 , and C 2 H 2 ) in large molecules [1-
3] can be found. The presence of conjugated π-electron systems in the molecule can
lead to a plasmon excitation in dependence of the collision energy [1, 3]. These
processes are extremely sensitive to the thermal energy associated with the various
internal degrees of freedom of the molecule. Studying these processes in a cryogenic
environment is essential to suppress excitation by black body radiation and rest gas
collisions.
The Cryogenic Storage Ring (CSR) [4] located at the Max-Planck-Institut für
Kernphysik (MPIK) in Heidelberg is an ideal experimental setup to perform collision
studies of photons and electrons with stored molecular ions at kinetic energies between
20-300 keV. The cryogenic temperature of about 10 K offers unique storage capabilities
in extreme vacuum conditions of below 100 rest-gas particles per cm3 and almost
vanishing blackbody radiation. A tunable optical parametric oscillator (OPO) laser
system allows photon interaction studies from the ultraviolet (225 nm) to the infrared
(2600 nm) regime. An Electrospray ion source setup in combination with a
radiofrequency quadrupole (RFQ) trap for ion accumulation, cooling, and bunching is
being developed to provide large molecular systems such as biomolecules for the CSR.
It is foreseen to study their ro-vibrational ground state properties, so far not possible in
room-temperature experiments. Further experiments aim to study decay rates of
metastable ions and radiative lifetimes.
References
[1] P. M. Mishra et al., Phys. Rev. A, 2013, 88, 052707.
[2] P. M. Mishra et al., Nucl. Instrum. Meth. B, 2014, 336, 12-18.
[3] P. M. Mishra et al., J. Phys. Chem. A, 2014, 118, 3128-3135.
[4] R. Hahn et al., Nucl. Instrum. Methods B, 2011, 269, 2871. |