catalysis; free jet; transition metal clusters; transition metal dimers; four-wave mixing; spectroscopy; laser-vaporization sources
Visser Bradley Beck Martin Bornhauser Peter, Knopp Gregor van Bokhoven Jeroen, Marquardt Roberto Gourlaouen Christoph Radi Peter (2017), Identification of a new low energy 1u state in dicopper with resonant four-wave mixing, in Journal of Chemical Physics
, 147(21), 214308-1-214308-10.
Beck M., Visser B., Bornhauser P., Knopp G., van Bokhoven J. A., Radi P. P. (2017), Rovibrational Characterization of High-Lying Electronic States of Cu 2 by Double-Resonant Nonlinear Spectroscopy, in The Journal of Physical Chemistry A
, 121(44), 8448-8452.
Kouzov A.P., Radi P.P. (2017), Line space theory of Resonant Four-Wave Mixing: New prospects for all-optical studies of photofragment states, in Chemical Physics Letters
, 673, 103-107.
Bornhauser P., Visser B., Beck M., Knopp G., van Bokhoven J. A., Marquardt R., Radi P. P. (2017), Experimental and theoretical investigation of the vibrational band structure of the 1(5)Pi(u)-1 (5)Pi(g) high-spin system of C-2, in JOURNAL OF CHEMICAL PHYSICS
, 146(11), 114309-1-114309-13.
Kouzov A, Radi P, Filippov N, Sinyakova T (2017), Helicity-induced shapes of resonant four-wave mixing responses from photofragments, in Journal of Physics: Conference Series
, 810, 012019-012019.
Visser B., Beck M., Bornhauser P., Knopp G., Gerber T., Abela R., van Bokhoven J. A., Radi P. P. (2016), Unraveling the electronic structure of transition metal dimers using resonant four-wave mixing, in JOURNAL OF RAMAN SPECTROSCOPY
, 47(4), 425-431.
Bornhauser P., Marquardt R., Gourlaouen C., Knopp G., Beck M., Gerber T., van Bokhoven J. A., Radi P. P. (2015), Perturbation-facilitated detection of the first quintet-quintet band in C 2, in The Journal of Chemical Physics
, 142(9), 094313-094313.
Spectroscopic experiments are proposed to assess the electronic structure and chemical bonding of small heteronuclear molecules containing the transition metal atoms zinc, copper, palladium and platinum. The results from the investigation of such alloys will contribute significantly to the knowledge on the elementary catalytic reaction mechanisms. The catalytic activity is of these metals is governed by the high density of low lying electronic states of these atoms. These states interact in a complex manner to form metal-metal and metal-ligand bonds. Accordingly, a dense and complicated electronic structure is present and spectroscopic studies thereof are extremely challenging.In contrast to conventional spectroscopic methods that have been applied in the past to gas phase species of transition metals such as resonant two-photon ionization, laser-induced fluorescence and to a lesser extend cavity ring-down and intracavity laser absorption, we suggest to apply non-linear four-wave mixing. This method has been shown (i) to be sufficiently sensitive in the low density environment of a molecular beam, (ii) to be applicable to non-fluorescing molecules and molecules exhibiting a short lifetimes in the excited state and (iii) to provide the possiblity of optical-optical double-resonance investigations. The latter feature is a significant advantage for the investigation of dense and complex spectra that are typically encountered in the study of transition metal compounds.The generation of the heteronuclear transition metal species will be performed by using a laser-vaporization source, either consisting of a rod or disk target. Some of the alloy samples are commercially available as rod or disks. Other samples will be produced by sputtering sources available at our institute. Fs-ionization mass spectrometry will be applied to carefully optimize the source parameters and to produce an abundance of the targeted species which is sufficient for spectroscopic studies. Improved cluster sources are important owing to the quadratic dependence of the four-wave mixing signal on number density in the beam. In addition, such improved sources are required for future experiments at the free electron laser (XFEL) being built at the Paul Scherrer Institute and for experiments using synchrotron radiation at the Swiss light source (SLS). Initially, degenerate and two-color resonant four-wave mixing experiments on the copper dimer are planned. The Cu2 diatom is well characterized and suited to establish the potential of the method. The high selectivity owing to intermediate level labeling is advantageous to disentangle the complex rotational spectra obtained by resonant two-photon ionization and LIF. The method has the potential of observing computed low lying electronic levels of ? symmetry and to shed light on perturbations occurring in the ground state of the molecule. These important issues could not be clarified up to now with standard spectroscopic techniques. Investigations on heteronuclear dimers and clusters are planned subsequently that contain zinc, copper, palladium and platinum atoms. The proposal describes typical problems and challenges that are encountered in spectroscopic studies of homonuclear transition metals. It is outlined how the application of non-linear four-wave mixing is favorable in situations where more conventional methods fail.Heteronuclear dimers and small clusters are much less investigated. Few measurements are available which contain the targeted species. The coexistence of different transition metals yields interesting electronic, geometrical, chemical and catalytic properties. To support the spectroscopic experiments electronic structure calculations are indispensable. A close collaboration is planned with a theoretical group lead by Prof. Roberto Marquardt at the university of Strasbourg, France.