Polycyclic aromatic hydrocarbons (PAHs) are abundant in many regions of the Universe, representing a major reservoir for cosmic carbon. However, their formation pathways in cold regions of space, such as dense molecular clouds and Titan's atmosphere, remain elusive despite the recent advances in the detection of aromatic molecules thereB.A. McGuire et al., Science 359, 202 (2018); B.A. McGuire et al., Science 371, 1265 (2021); J. Cernicharo et al., A&A 649, L15 (2021) Astronomical observations show that astrochemical models significantly underestimate the abundance of these aromatic molecules, indicating that efficient formation pathways, such as ion-molecule reactions involving aromatic ions and hydrocarbon neutrals, are likely missing in the existing models.
In our work, we use a cryogenic 22-pole ion trap apparatusP. Jusko, S. Brünken, O. Asvany, S. Thorwirth, A. Stoffels, L. van der Meer, G. Berden, B. Redlich, J. Oomens, and S. Schlemmer, Faraday Discuss. 217, 172 (2019)o study ion-molecule reactions at low temperature, and to structurally identify ionic reactants, reaction intermediates and products in-situ employing infrared-predissociation (IRPD) and infrared multiple-photon dissociation (IRMPD) spectroscopy using the infrared free-electron lasers at the FELIX Laboratory. We reveal efficient low-temperature formation pathways towards PAHs and related species via exothermic ion-molecule reactions. The experimental approach combines kinetic and spectroscopic studies, and unambiguously identifies key reaction intermediates, and, in the case of the reaction of pyridine⁺ with acetylene, the final nitrogen-containing PAH product ion quinolizinium⁺.D.B. Rap, J.G.M. Schrauwen, A.N. Marimthu, B. Redlich, and S. Brünken, Nat. Astron. 6, 1059 (2022)hese studies not only reveal competing formation pathways relevant in cold astronomical environments, but also deliver a variety of information to verify in-silico potential energy surfaces, astronomical models, and to guide infrared observations.

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B.A. McGuire et al., Science 359, 202 (2018); B.A. McGuire et al., Science 371, 1265 (2021); J. Cernicharo et al., A&A 649, L15 (2021). P. Jusko, S. Brünken, O. Asvany, S. Thorwirth, A. Stoffels, L. van der Meer, G. Berden, B. Redlich, J. Oomens, and S. Schlemmer, Faraday Discuss. 217, 172 (2019)t D.B. Rap, J.G.M. Schrauwen, A.N. Marimthu, B. Redlich, and S. Brünken, Nat. Astron. 6, 1059 (2022)T

The tandem cryo ion trap FRITZ allows the investigation of organometallic complexes as well as transition metal cluster ions in the gas phase with adsorbed reaction gases. The setup enables studies on uptake kinetics as well as IR-PD action spectroscopy under cryo conditions. In this talk we present studies of dinitrogen adsorbed to transition metal cluster anions and cations with regard to the elementary steps of N2 activation. Supported by DFT modeling we aim to explain the influence of geometric and electronic features of the transition metal cluster ions to the N2 activation process.

Proton-coupled electron transfer (PCET) processes are vitally important throughout chemical and biochemical catalysis. While electron transfer kinetics have been well studied, direct interrogation of the proton transfer coordinate has remained largely unexplored. We present cryogenic ion vibrational spectra of a series of phenol-benzimidazole and phenol-pyridine PCET model dyads to explore the nature of the strong OH-N H-bond in the ground electronic state. Highly red shifted and asymmetrically broadened H-bonded OH stretch transitions are observed throughout the model series, while the deuterated isotopologues yield much weaker OD stretch transitions that are more symmetrically broadened. To explain the origins of the spectral broadening, we employ a computational model that couples the two-dimensional potentials describing the stretching and in-plane bending degrees of freedom of the shared H atom to the remaining vibrational degrees of freedom. These two-dimensional potentials are predicted to be very shallow along the H atom transfer coordinate, enabling significant dislocation of the H atom between the donor and acceptor groups upon excitation of the OH vibrational modes. These soft H atom potentials result in strong coupling between the OH modes, which exhibit extensive bend-stretch mixing, and a large number of normal mode coordinates. Vibrational spectra are calculated using a Hamiltonian that linearly and quadratically couples the H atom potentials to over thirty of the most strongly coupled normal modes treated at the harmonic level. The calculated vibrational spectra qualitatively reproduce the shape and breadth of the experimentally observed bands in both isotopologues. The results highlight a unique broadening mechanism and complicated anharmonic effects present within these biologically relevant PCET model systems.

Infrared predissociation action spectroscopy in its form as messenger spectroscopy, is a well-established technique to record vibrational spectra of reactive molecular ions. One of its major drawbacks is that the spectrum of the messenger-ion complex is taken as a proxy of that of the bare ion. In particular for small open-shell species, such as the Renner-Teller (RT) affected HCCH⁺, the attachment of the tag may have a significant impact on the spectral features. In order to investigate this effect, we have recorded the vibrational spectra of Ne- and Ar-tagged HCCH⁺ using a cryogenic ion trap end user station at the FELIX laboratoryJusko, P.; Brünken, S.; Asvany, O.; Thorwirth, S., Stoffels, A. et al.. Faraday Discuss., 2019, 217, 172-202. and compared them to previous data of the bare ion obtained with laser induced reactions (LIR) spectroscopySchlemmer, S.; Asvany, O.; Giesen, T. Phys. Chem. Chem. Phys., 2005, 7(7), 1592-1600. The Ne-attachment led to a shift in band positions and change in relative intensities, while the Ar-attachment even led to a complete quenching of the RT splitting. Whereas for HCCH⁺ LIR offers a tag-free spectroscopic method^b, this is not the case for most other reactive open-shell species. The newly developed leak-out spectroscopy (LOS)Schmid, P. C.; Asvany, O.; Salomon, T.; Thorwirth, S.; Schlemmer, S. J. Phys. Chem. A, 2022, 126(43), 8111-8117 seems to provide a much more universal tag-free method. Here we present the application of this method to record the cis-bending of the HCCH⁺ cation ( 700 cm⁻¹), and demonstrate that the obtained LOS spectrum is equivalent to the previously recorded LIR spectrum. Not only presents this the energetically lowest-lying vibrational mode targeted with LOS so far, but it also shows its potential to overcome the tag problem in other Renner-Teller affected species.

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Jusko, P.; Brünken, S.; Asvany, O.; Thorwirth, S., Stoffels, A. et al.. Faraday Discuss., 2019, 217, 172-202., Schlemmer, S.; Asvany, O.; Giesen, T. Phys. Chem. Chem. Phys., 2005, 7(7), 1592-1600.. Schmid, P. C.; Asvany, O.; Salomon, T.; Thorwirth, S.; Schlemmer, S. J. Phys. Chem. A, 2022, 126(43), 8111-8117,

Alkyl and aryl cobinamides are close relatives to adenosylcobalamine, vitamin B12, which is an essential cofactor for a large number of enzymatic transformations. We report gas-phase investigations of the Co-C bond strength by means of energy-resolved collision-induced dissociation experiments, which found unexpected discrepancies to predictions made by dispersion-corrected DFT. Attempted resolution of the discrepancies led us to further cobinamide derivatives, whose ion spectroscopy provide key information on the gas-phase structure of these large molecules ( ca. 150 atoms). The structural considerations lead to a hypothesis for the mechanism of control and regulation of vitamin B12 in the enzymatic reactions.

The high-resolution rovibrational and pure rotational spectra of H₂C₃H⁺ are reported here for the first time. The spectra were collected in a 4K 22-pole cryogenic ion trap (COLTRAP) instrument using the novel leak-out spectroscopy (LOS) method.Schmid, P. C., Asvany, O., Salomon, T., Thorwirth, S., and Schlemmer, S. 2022, J. Phys. Chem. A, 126, 8111.ovibrational signatures within the fundamental ν₁ (C-H stretch) and the combination ν₃+ν₅ (C-C stretches) bands were detected in the 3 μm spectral region using a continuous wave optical parametric oscillator and were successfully assigned, aided by previous theoretical calculations.Huang, X., Taylor, P. R., and Lee, T. J. 2011, The Journal of Physical Chemistry A, 115, 5005.hese observations allowed accurate spectroscopic constants for the ground and vibrationally excited states to be determined. Significant differences were observed in the values of the rotational constant A, which decreases by about 2.7% and 5.0% in the ν₁ and ν₃+ν₅ bands, respectively, in comparison to ν₀. By analyzing the changes in A, information about the molecular structure of H₂C₃H⁺ upon excitation of the C-H and C-C stretches was obtained, which indicates that the HCH angle may have an increase of approximately 3^° in ν₁ and 6^° in ν₃+ν₅. Guided by the ground state constants obtained from the infrared (IR) measurements, 14 pure rotational lines were observed in the 90-200 GHz frequency range using a double resonance scheme, in which the ions are excited simultaneously by the IR and a mm-wave radiation. These rotational measurements allowed even more accurate ground state spectroscopic parameters to be determined and open up the possibility for the first (radio)astronomical search of H₂C₃H⁺ in the interstellar medium. Finally, the capability of the novel LOS method in isolating isomers in the ion trap will be discussed with a focus on the abundances of H₂C₃H⁺ and its cyclic sibling, c-C₃H₃⁺.

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Schmid, P. C., Asvany, O., Salomon, T., Thorwirth, S., and Schlemmer, S. 2022, J. Phys. Chem. A, 126, 8111.R Huang, X., Taylor, P. R., and Lee, T. J. 2011, The Journal of Physical Chemistry A, 115, 5005.T

High-resolution ro-vibrational spectra of the C-C stretching fundamentals of C₃H⁺, NCCO⁺, and HC₃O⁺ are recorded using the leak-out action spectroscopy method in the 22-pole ion trap apparatus COLtrap II. In this experiment parent ions are mass selected prior to storing them in the cryogenic ion trap. Here they are cooled to the ambient temperature by collisions with a pulse of Helium buffer gas. A mode-hop-free quantum cascade laser emitting at around 5μm is used to excite the desired molecular vibrations. N₂ is used as second collision partner which is provided continuously to the cold trap. The trap is kept at a nominal temperature of 40 K in order to avoid freezing of the gas. The vibration to translation (V-T) energy transfer of the excited ions leads to a loss of those ions via an electrostatic barrier at the exit electrode. A spectrum is recorded with high S/N ratio by measuring the number of lost ions as a function of the excitation frequency. Nicely resolved P- and R- branches for the three linear molecular ions are observed with rotational, i.e. collisional temperatures slightly larger than the trap temperature and with line widths slightly exceeding the corresponding Doppler-widths. Accurate molecular parameters are determined from these measurements. Thanks to the high sensitivity of our experimental approach also hot-band transitions as well as combination bands can be identified in favorable cases. Results from these experiments will be presented.

The success of future missions to search for life on ocean/icy worlds or investigate organic molecule rich planetary atmospheres depends on the ability to accurately identify and quantify biomarkers in the presence of a mixture of molecules.The authors gratefully acknowledge support from a JPL/NASA Strategic University Research Partnership Grant, as well as helpful discussions with Madison Foreman (JILA), Dr. Frank Maiwald (JPL), Dr. Robert Hodyss (JPL), and Dr. Deacon Nemchick (JPL).ass spectrometry alone is insufficient to unambiguously identify biomarkers due to the existence of isomers, but combined with infrared spectroscopy additional information can be extracted. Amino acids are a prime target in the search for biomarkers due to their importance in terrestrial biology. Here, we present cryogenic gas-phase infrared spectra of protonated valine and some chemical analogs. We assign spectral features using density functional theory calculations, and we discuss prospects for chemical identification.

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The authors gratefully acknowledge support from a JPL/NASA Strategic University Research Partnership Grant, as well as helpful discussions with Madison Foreman (JILA), Dr. Frank Maiwald (JPL), Dr. Robert Hodyss (JPL), and Dr. Deacon Nemchick (JPL).M

Polycyclic aromatic hydrocarbons (PAHs) play an important role in the chemistry of the interstellar medium. The recent unambiguous detection of several comparably small PAHs in the cold interstellar medium through radioastronomical observationsMcGuire et al. Science 2021 371 1265, Cernicharo et al. A&A 2021 649 L15as rekindled the interest in spectroscopic studies of PAHs consisting of only two or three aromatic rings and their derivatives. In this work, the vibrational spectra of indenyl and fluorenyl anions has been studied by infrared predissociation (IRPD) action spectroscopy using the Free Electron Laser for Infrared eXperiments, FELIX, at Radboud University, in combination with the cryogenic 22 pole ion trap setup FELionJusko et al. Faraday Discuss. 2019 217 172 The range of 650 - 1650 cm⁻¹ was sampled by measuring the depletion of the signal of the H₂-tagged ion as a function of the laser wavelength. High-level quantum-chemical calculations at the CCSD(T) level of theory have also been performed for the spectroscopic assignment of the detected vibrational bands.

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McGuire et al. Science 2021 371 1265, Cernicharo et al. A&A 2021 649 L15h Jusko et al. Faraday Discuss. 2019 217 172.

We report the first infrared spectra taken of single trapped molecular ions. Analyzing samples one molecule at a time allows for fundamentally different approaches to chemical analytics than is possible in the usual ensemble case, where chemical separation is often a prerequisite for resolving complex mixtures. Briefly, a single molecular ion is repeatedly tagged with an N2 molecule and detagged via infrared excitation, and these events are detected via non-destructive mass spectrometry via a co-trapped atomic ion. Extensions to ion chemistry, mixture analysis, precision measurement, and spectroscopy of radicals will be presented.