UNIVERSITÄT ZU KÖLN

Investigators

• Sven Thorwirth
• Thomas Salomon
• John B. Dudek (Hartwick College)

Description

Carbonaceous clusters are of importance in diverse scientific areas such as astrochemistry, material science, structural chemistry and theoretical chemistry. Pure carbon clusters have been observed in space by their characteristic infrared spectroscopic fingerprints. Additionally, small polar sulfur- and silicon-carbon clusters have been identified in space also by their pure rotational spectra, most prominently in the circumstellar shells of the prototypical late-type star IRC+10216. It is high-resolution laboratory spectroscopy having the great potential to provide information on the structures of individual clusters, to provide reference data for astronomical identification and to benchmark data for evaluation of the performance of quantum-chemical methods.

Methods

Carbonaceous clusters are produced through laser ablation. High-energy UV laser pulses (355 nm) are focused onto a rotating rod composed of appropriate precursor material (graphite, SiC, etc.). Products are carried through a 1cm reaction channel by pulses of Helium gas kept at a backing pressure of 10-20 bar and expand adiabatically into the vacuum chamber. The background pressure in the vacuum chamber is kept below 0.1 mbar. With every single laser pulse a total amount of roughly 10¹³-10¹⁴ clusters of different sizes is produced.

Molecules are investigated at high spectral resolution using infrared radiation provided by quantum cascade lasers or optical parametric oscillators.

Carbon Cluster Experiment

In the carbon cluster experiment, part of the infrared probe radiation is guided through a reference gas cell and a reference interferometer for calibration purposes. The major fraction is guided into a vacuum chamber and through a Herriott-type multireflection cell where it is intersecting the free jet harboring the clusters perpendicularly close to the exit of a slit nozzle. After having passed the chamber, the infrared beam is detected using sensitive InSb or HgCdTe detectors and its signal is digitized using an USB oscilloscope.

• Experimental and quantum-chemical characterization of heavy carbon subchalcogenides: Infrared detection of SeC3Se
  T. Salomon, J. B. Dudek, Y. Chernyak, J. Gauss, and S. Thorwirth,
  J. Mol. Spectrosc. 378, 111456 (2021).

• A continued investigation of carbon subsulfide, SCCCS, at 5mum: New hot bands and isotopic species
  T. Salomon, J. B. Dudek, S. Bentley, S. Schlemmer, and S. Thorwirth
  J. Mol. Spectrosc. 356, 21-27 (2019).

• High-resolution infrared fingerprints of carbon-sulfur clusters: The v1 band of C5S
  S. Thorwirth, T. Salomon, S. Fanghänel, J. R. Kozubal and J. B. Dudek
  Chem. Phys. Lett. 684, 262-266 (2017).

• Carbon-sulfur chains: A high-resolution infrared and quantum-chemical study of C3S and SC7S
  J. B. Dudek, T. Salomon, S. Fanghänel, and S. Thorwirth,
  Int. J. Quantum Chem. 117, e25414 (2017).

Acknowledgments

Funding by the Deutsche Forschungsgemeinschaft through grant SFB 1601, and TH1301/3-2 is gratefully acknowledged.