The work in Professor Bondybey's group at the Technical University
of Munich in Garching focusses on structure and reactivity of molecules,
and molecular and ionic clusters. Four state of the art experiments are
used for spectroscopic and kinetic studies:
1. The FTIR matrix isolation experiment, a Bruker IFS 120 Fourier transform spectrometer together with high resolution laser systems and cryostats down to 4 K, was recently extended with a mass-selection stage for the size-selective deposition of molecular and cluster ions in low temperature rare gas matrices. Initially we concentrated on the investigation of radicals and molecular ions, using our gas discharge source to produce the molecules of interest in rare gas matrices like neon or argon. Lateron we developed a laser vaporization source to obtain clusters of even the most refractory materials.
2. The FT-ICR mass spectrometer Spectrospin CMS47X is equipped with a 4.7 Tesla superconducting magnet, a Bruker Infinity Cell and a home-built additional source chamber for the operation of ion sources with a high gas load. The most powerful ion source in use in our laboratory is a pulsed laser vaporization source, where ions are produced by a 5 ns laser pulse and cooled and clustered in the supersonic expansion of a 50 us gas pulse provided by a homebuilt piezoelectric valve. It is the main instrument used for laboratory studies of atmospheric chemistry, since cationic and anionic water clusters and hydrated ions can serve as model systems for polar stratospheric clouds. The reactivity of these nano-sized "ice" particles can be unambiguously probed in the ICR cell.
3. Our ZEKE experiment was recently extensively modified to further improve its resolution, and to also permit MATI spectroscopy. Our interests are determination of ionization potentials, vibrational modes and structure enlightenment of ions and small ionic clusters by pulsed field ionization following nonresonant one color, two photon excitation. Furthermore we are interested in dissociation dynamics were we picture the dynamic of the intermediate state along the dissociative coordinate to an ionic final state before the dissociation is completed. The for our experiments necessary cold molecules are provided by a molecular expansion in a high vacuum chamber.
4. Studies of simple metal-contaning molecules or small metal clusters are essential compomparts of our quest for a deeper understanding of chemical bonding. Convenient techniques for spectrosopic studies like LIF (laser-induced fluorescence) or REMPI (resonance-enhanced multi-photon ionisation) have been applied for studies of a large number of systems. Unfortunately, as a consequence of rapid nonradiative processes and fragmentation, these techniques frequently fail when the size of the cluster or molecule studied exceeds a few atoms. The instantaneouse density of the atoms and molecules produced by a laser vaporization source is high, and absorption spectroscopy is an obvious alternative. Therefore we combined laser vaporization with cavity ringdown laser absorption spectroscopy (CRLAS) to provide an extremely sensitive detection of a variety of cluster species. In the CRLAS technique the jet with the absorbing species to be investigated is located inside a high-finesse optical cavity consisting of two highly reflecting mirrors. A fraction of the tunable probe laser pulse enters the cavity through one of the mirrors, and then propagates with gradually decreasing intensity back and forth inside the cavity. With each reflection a small fraction of the photons leaks out through the highly reflecting mirrors. If the laser is tuned to a frequency where the molecular species in the jet absorb, the cavity losses are increased and this is evidenced by the shortened ringdown time. We have recently used our laser vaporization source to investigate a number of highly refractory species, including tungsten and tungsten oxides. The combination of the very high sensitivity of CRLAS and the flexibility in producing metal-containing molecules with the laser vaoprization technique opens us great perspectives in spectroscopy research.
The experimental studies are complemented by high-level electronic structure calculations. We have access to the program packages Gaussian98 and Molpro96, which are installed on various platforms including DEC Alphastation500 and SGI Power Challenge. For more-than-routine jobs, the super computers at the Leibniz Rechenzentrum are also available.