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Molecular Networks with precision Terahertz Spectroscopy

Final Report Summary - MONTES (Molecular Networks with precision Terahertz Spectroscopy)

Within this project the spectroscopy of cold, trapped molecular ions in the terahertz domain, detected by purely optical means, has been developed and implemented. Several molecular ions could be studied with the approach.

During the first part of the project, rotational quantum state diagnostics was implemented for hydroxyl anions trapped in a radiofrequency ion trap. This was achieved using a frequency-tunable laser to selectively neutralize the negative ions. In parallel to this work, the characterization of the terahertz source, which delivers widely tunable radiation over a spectral range from 100 to 1600 GHz, was carried out. Bringing these two techniques together allowed us to successfully perform the terahertz spectroscopy on trapped molecular anions using the purely optical detection scheme.

In order to perform spectroscopy on larger, biomolecular ions, a novel ion trap setup combined with electrospray ionization was constructed. In this sixteen-pole wire trap we have trapped a range of different protonated amino-acids and have implemented the tagging technique using both hydrogen and helium. With up to six hydrogen molecules attached to protonated tryptophan, we have performed vibrational action spectroscopy in the near infrared and investigated the influence of the attached hydrogen molecules on the vibrational motion of the amino acid.

Finally, terahertz spectroscopy with optical detection was applied for the first time to a triatomic molecular anion, the amide anion NH2-. Near-threshold photodetachment experiments revealed a scheme for rotational state-dependent probing of this ion. A spectral search has then produced the transition near 934 GHz. Since this ion is of great interest for the nitrogen chemistry in interstellar clouds our results are crucial to clarify the existence of this ion in interstellar space.

In further work, we employed the rotational state analysis method to study rotationally inelastic collision rate coefficients of hydroxyl anions and their deuterium-containing counterparts upon interaction with cold helium atoms. We have also investigated the properties of interstellar carbon chain anions and performed electronic spectroscopy on helium-tagged fullerene cations.