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A symposium entitled "Infrared Free-Electron Lasers: The State of the Art 2024" will bring together machine scientists and users of IR FELs to celebrate 10 years of the FHI FEL Facility as well as the successful commissioning of the 2-color FHI FEL Upgrade. It will take place from July 28th to 31st, 2024 in the Harnack Haus next to the FHI campus in Berlin, Germany.
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2-color user experiments
Group Foto by Marco De Pas
Preparations for a linac based THz source installation are underway at the National Centre for Nuclear Studies, Świerk in Poland. The superconducting linac based on two Rossendorf-like accelerating cryomodules and including all superconducting electron gun, has been designed in order to deliver 20 pC – 250 pC electron bunches to the 8 × 160 mm planar, permanent magnets, variable gap undulator, in cw, up to 50 kHz repetition, mode of operation. The THz source will be accompanied with solid state and plasma jet sources of IR - EUV ranged radiation and with an MeV ranged UED beamline. Currently the major components procurement is being completed, the installation will begin in the half of 2025 aiming at the commissioning and first light in 2026. The efforts to provide a wide range tunable and coherent electromagnetic radiation source dedicated for fundamental and applied sciences are, on the other hand, intended as an introductory step in FEL science and engineering development in Poland.
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2-color user experiments
Kiriliouk Group
Cryogenic ion-trap vibrational spectroscopy is a valuable method to study molecular structure and the strength of inter- and intramolecular interactions. The Asmis group uses infrared photodissociation (IRPD) spectroscopy on mass-selected clusters in the gas phase, making use of the Free Electron Laser at the FHI, to study their structure, reactivity and dynamics, with the goal to bridge the knowledge gap between isolated, small particles in the gas phase and condensed matter. Two main projects are developed at the FHI-Asmis group, i. metal oxide clusters in the gas phase and ii. chiral selector IRPD spectroscopy.
The understanding of heterogeneous catalysis cannot be achieved without experimental model catalysts that reduce the complexity of supported metal or metal oxide catalysts. Therefore, metal oxide clusters in the gas phase are aimed at gaining a better atomistic understanding of single-site catalysts. Our group has many years of expertise on combining state-of-the-art mass spectrometric and infrared spectroscopic experiments with quantum chemical calculations to ultimately gain molecular-level insights into the geometric structure of, and C-H and O-H bond activation by mixed metal oxide clusters.
The second area aims to study chiral selector IRPD spectroscopy. The handedness of drugs, agrochemicals and flavors is crucial for their properties and characterization methods that can recognize, distinguish and quantify enantiomers are required. We transfer chiral analytes present in an enantiomeric mixture into the gas phase, where they form complexes with a volatile chiral selector. The respective diastereomers can be spectrally differentiated and the enantiomeric excess in solution is determined by this gas phase approach, with minimal sample and time consumption, and with satisfactory accuracy.
Future studies of these and related systems will make use of an instrument upgrade that will add a mass selection and reaction stage to our current setup. This will allow to perform reactions at different temperatures, at different partial pressures and with different gases. Also, reaction product ions are mass- selected before they are trapped, adding another stage of selectivity to the experiment.
FELIX-2 upgrade; small molecule identification (and its lab infrastructure), with identification for Police
Organometallic ion complexes provide models for catalytic processes, and they have been implicated as important species in astrochemistry, perhaps as carriers of optical signals such as the diffuse interstellar bands (DIBs). In the present work, we investigate the properties of transition metal cation complexes with acetylene or benzene molecules using a combination of infrared and UV-visible laser photodissociation spectroscopy. Ion-molecule complexes of the form M+(C2H2)n and M+(benzene)n are produced by laser vaporization in a pulsed-nozzle supersonic beam source. The ions are analyzed and selected by mass in a reflectron time-of-flight mass spectrometer. Vibrational spectroscopy measurements are performed with infrared photodissociation spectroscopy, using an IR-OPO laser and the method of "tagging" with argon atoms to enhance dissociation yields [1]. Electronic spectroscopy experiments use photodissociation with a UV-visible OPO laser system.
Infrared experiments investigate complexes of vanadium, platinum and iron with acetylene. This work establishes that the M+(C2H2) complexes have cation-π structures, with the metal cation located in a symmetric position above the triple bond of acetylene. Charge-transfer interactions cause the C‒H stretch vibrations to shift to lower frequencies compared to those in the free acetylene molecule. Multiple-acetylene complexes of iron or platinum reveal interesting coordination structures, but no intracluster reactions. Vanadium ion complexes with three or more ligands undergo intracluster reactions to form the metal ion-benzene complexes.
UV-visible spectroscopy on Fe+(C2H2), Fe+(benzene) and Fe+(benzene)2 find spectra that are quasi-continuous throughout the visible wavelength region, eliminating these ions as candidates to explain DIB spectra [2,3]. The energetic threshold where photodissociation first occurs provides the metal ion-ligand bond energy. Additional experiments employ the method of photofragment imaging to investigate the energetics of the cation-π bonds which form in these complexes [2,3]. Photodissociation thresholds and photofragment imaging measurements are in agreement on the cation-molecular bond energies in these complexes, and the values obtained also agree with previous results from collisional dissociation experiments.
References
[1] A. D. Brathwaite, J. H. Marks, I. J. Webster, A. G. Batchelor, T. B. Ward, M. A. Duncan, J. Phys. Chem. A 126, 9680 (2022).
[2] J. E. Colley, N. J. Dynak, J. R. C. Blais, M. A. Duncan, J. Phys. Chem. A 127, 1244 (2023).
[3] J. E. Colley, N. J. Dynak, J. R. C. Blais, M. A. Duncan, J. Phys. Chem. A 127, 2795 (2023).
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2-color user experiments
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