Testing the strong PAH Hypothesis

• Applicant: Professor Dr. Stephan Schlemmer, since 4/2021
• Subject Area: Astrophysics and Astronomy ; Optics, Quantum Optics and Physics of Atoms, Molecules and Plasmas
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433563256

We propose to test the strong PAH hypothesis by obtaining pure rotational spectra as well as ro-vibrational spectra of polycyclic aromatic hydrocarbons (PAHs) and related cyclic molecules. This laboratory work shall provide spectroscopic data which for the first time would enable to identify this important class of molecules in space.The experiments will be conducted using a manifold of dedicated instrumental techniques spanning a wide frequency range.Two state-of-the-art heterodyne emission spectrometers have been designed, built and tested specifically to record spectra of excited molecules.These instruments are the first of their kind and are operational between 75 and 110 GHz and between 300 and 400 GHz coincident with two bands (bands 3 and 7) of the world leading Submillimeter telescope ALMA (Atacama Large Millimeter/submillimeter Array).Additionally, very sensitive absorption spectrometers extend the available frequency range well above 1 THz, where some of the low frequency vibrational bands of PAHs lie.Within this proposal we will also build a new absorption experimentusing a high-power high-bandwidth amplifier-multiplier chain operational up to 2 THzto allow for high-resolution spectroscopy of the fingerprint-like ro-vibrational states of PAHs.Finally, the unique emission spectrometer of the SOFIA upGREAT lab setup located in-house at the University of Cologne will be utilized to search for the ro-vibrational fingerprints of PAHs in emission near 2 THz. Access to the SOFIA upGREAT lab setup is granted by my collaborator Dr. Honingh.The laboratory spectroscopy of pure PAH species, substituted PAHs as well as other cyclic molecules will be in the focus of this stuy. In addition, spectra of fragments of PAHs and other cyclic molecules will be recorded to address the other fundamental question about the formation and destruction processes of PAHs which is discussed in the scientific community as the bottom-up or top-down chemistry approach, respectively.On the long term the expected spectra can be directly compared to spectra taken with the ALMA telescope and the SOFIA-(Stratospheric Observatory for Infrared Astronomy) airborne telescope.In summary, this proposal shall address the long standing problem on the identification of PAHs as one of the key species in the interstellar medium and how those molecules are formed.

• DFG Programme: Research Grants
• Major Instrumentation: Amplifier/Multiplier-Chain
• Instrumentation Group: 6140 Verstärker und -Module der Digitalelektronik, Impulsformer
• Ehemalige Antragstellerin: Dr. Nadine Wehres, until 3/2021