Silicon is very important in the modern electrical industry, for example for the production of solar cells. To improve their efficiency the newest generation of solar cells consists of nanostructures like quantum dots. Therefore studies about optical properties of silicon nanoclusters are of particular interest [1]. These characteristics for the smallest cluster Si₂, which is necessary for the formation of larger clusters, are not well established yet [1].
In this talk, experimental data and quantum chemical calculations on the absorption and dissociation properties of Si₂⁺ are presented. The spectrum of Si₂⁺ was obtained by photodissociation of mass-selected Si₂⁺ cations in a tandem mass spectrometer, which are created in a laser vaporization source [2]. The experimental results are compared and discussed with theoretical results of TD-DFT calculations. Significantly, our optical spectrum provides the first spectroscopic information for this simple diatomic cation.
Literature:
[1] L.-Z. Zhao et al. J. Phys. Chem. A 2017, 121, 34, 6388–6397 [2] M. Förstel et al., Rev. Sci. Instrum., 2017, 88, 123110.

l0pt Figure Silicon oxide cluster cations Si_nO_m⁺ are especially interesting in the context of interstellar dust particles and might be carriers of the diffuse interstellar bands (DIBs). To date, SiO and different Si_nC_m clusters were found in circumstellar envelopes. In this talk we present our results on the fairly small but nevertheless complicated Si₃O₂⁺ system. We discuss the optical spectrum obtained by photodissociation in the gas phase and compare that to quantum chemical calculations. Spoiler, the observed spectrum of Si₃O₂⁺ does not match any known DIB.

The linear N ≡ C−C ≡ O⁺ ion has been studied spectroscopically for the first time using the Free Electron Laser for Infrared eXperiments, FELIX, at Radboud University (Nijmegen, The Netherlands) in combination with the 4K 22-pole ion trap facility FELion.Jusko et al. 2019, Faraday Discuss. 217, 172he vibrational spectrum of NCCO⁺ was observed in the range from 500 to 1500 and 2000 to 2500 cm⁻¹ using resonant photodissociation of the correponding Ne-complex while monitoring the depletion of the ion-Ne cluster signal as a function of wavenumber. Spectroscopic assignment of vibrational bands relies on comparison against results from high-level quantum-chemical calculations performed at the CCSD(T) level of theory and very good agreement is found. Jusko et al. 2019, Faraday Discuss. 217, 172T

Diatomic molecules RgM consisting of a rare-gas atom Rg and an alkaline-earth-metal atom M and their singly and doubly-charged cations RgM⁺ and RgM²⁺ have unusual chemical properties that are related to the low first and second ionization energies of M and the high ionization energy of Rg. In MgAr the second ionization energy of Mg is lower than the first ionization energy of Ar. Consequently, MgAr²⁺ is thermodynamically stable and Rydberg series of MgAr⁺ can be observed that converge on the X^{2+   1}Σ⁺ ground state of MgAr²⁺.D. Wehrli, M. Génévriez and F. Merkt, Phys. Chem. Chem. Phys., 23, 10978, (2021) and references thereinn this contribution, we present the results of spectroscopic investigations of MgKr⁺ in its ground and low-lying electronically excited states that complement earlier studies of this cation.J. G. Kaup and W. H. Breckenridge, J.Chem. Phys. 107, 2180, 1997^,J. S. Pilgrim, C. S. Yeh, K. R. Berry, M. A. Duncan, J. Chem. Phys., 100, 7945, (1994)ulsed−field−ionization zero−kinetic−energy (PFI−ZEKE) photoelectron spectra of the X^+ ^2^+ ground state of MgKr^+ were recorded following single−photon excitation from the a  ^3_0 metastable state of MgKr. Vibrational channel interactions enabled the observation of the lowest vibrational levels of MgKr^+ and the determination of an accurate value of the adiabatic ionization energy of metastable MgKr (38183 2  ^-1). Using isolated−core multiphoton Rydberg dissociation (ICMRD) spectroscopy,M. Génévriez, D. Wehrli and F. Merkt, Mol. Phys. 118, e1703051 (2019)pectra of several low−lying electronically excited states of MgKr^+ were observed that are associated with the Kr + Mg^+ (nl) dissociation limits with n=3,4 and l=s, p and d. These states may be regarded as the lowest members of Rydberg series converging on the ground state of MgKr^2+. These studies represent first steps towards studying the doubly charged cation MgKr^2+ J. S. Pilgrim, C. S. Yeh, K. R. Berry, M. A. Duncan, J. Chem. Phys., 100, 7945, (1994)PM. Gnvriez, D. Wehrli and F. Merkt, Mol. Phys. 118, e1703051 (2019)s

The C₃H⁺ ion has been identified as an important reaction intermediate in the carbon chemistry network in the interstellar medium and was recently detected via its rotational linesJ. Pety et al., A&A 548(2012)A68., B. McGuire et al., Ap. J. 774(2013)56. Laboratory measurements on the rotational spectrum of linear C₃H⁺ provided accurate spectroscopic parameters for the vibrational ground stateS. Brünken et al., Ap. J. Lett. 783(2014)L4. In addition, vibrational pre-dissociation spectroscopy of the linear C₃H⁺-Ne complex offered first insights on the vibrational band positions of this moleculeS. Brünken et al., J. Phys. Chem. A 123(2019)8053.
Here, we report on the first infrared study of C₃H⁺ at high spectral resolution that was targeted at the C−H stretching mode ν₁ located around 3170 cm⁻¹. The experiment was performed in our cryogenic multipole 22-pole ion trap instrument LIRtrap. In addition to the vibrational fundamental, the associated ν₁+ν₅ ← ν₅ hot band originating from the energetically lowest bending mode could be detected. Both spectra are in good agreement with estimates based on previous quantum-chemical calcultions and low-resolution measurements.

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Footnotes:

J. Pety et al., A&A 548(2012)A68., B. McGuire et al., Ap. J. 774(2013)56.. S. Brünken et al., Ap. J. Lett. 783(2014)L4.. S. Brünken et al., J. Phys. Chem. A 123(2019)8053..

Charge transfer electronic spectroscopic results were reported for the Ag+-benzene complex in the gas phase using photodissociation. The Ag+-benzene complex was generated by laser vaporization of a silver rod in combination with pulsing an inert gas seeded with benzene then mass selected and probed using a time-of-flight mass spectrometer. The mass-selected ions were then fragmented and scanned using a solid state OPO capable of scanning through the UV-Visible range. A high-resolution electronic spectrum of Ag+-benzene was reported in the UV-Visible range to determine the upper threshold for the dissociation energy of the Ag+-benzene complex which were compared with previous velocity map imaging results. An unexpected feature was observed in the lower UV region which was attributed to the HOMO-LUMO absorption on an excited benzene ligand.

We present high-resolution infrared action spectra of cold H₅O₂⁺. For this purpose the mass selected parent ions are stored in a cryogenically cooled 22-pole ion-trap (COLtrap). There we employ a two-color-photodissociation scheme where first the symmetric or the anti-symmetric O-H-stretching band is excited by a narrow linewidth cw-OPO. Then, Light from a CO₂ laser is used to efficiently dissociate the parent molecule. The infrared-absorption of the parent ion is recorded by the appearance of H₃O⁺ photoproducts. This procedure follows the seminal approach first invented in the group of Y.T. Lee ^a,b. The rotationally resolved and basically background-free spectrum exhibits a complex structure, making the assignment of individual ro-vibrational tunneling features challenging. Nonetheless, recurring spectral spacings are used to start to unfold the rotational/tunneling structure. Moreover, spectral indicators are found that support the assumption of hydrazine-like tunnelling dynamics being present in this peculiar molecule of fundamental interest.

^a L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee , Vibrational spectroscopy of the hydrated hydronium cluster ions H₃O⁺(H₂O)_n (n=1,2,3), J. Chem. Phys. 91, 7319-7330 (1989)

^b L. I. Yeh, Y. T. Lee, and J. T. Hougen. Vibration-rotation spectroscopy of the hydrated hydronium ions H₅O₂⁺ and H₉O₄⁺. Journal of Molecular Spectroscopy 164.2 (1994): 473-488.

The activation and utilization of N₂ have become attractive areas of research, with the ultimate goals of dinitrogen fixation and reduction. A deep understanding of the interaction and electronic influences between transition metal atoms and the inert N2 molecule would allow facilitating the transformation of inert molecular nitrogen to useful nitrogen-containing chemicals. In this work, we used cryogenic ion vibrational predissociation (CIVP) spectroscopy to experimentally probe the activation of the molecular nitrogen by copper complexes bearing terpyridine and pyridine-2,6-bis(oxazoline) ligands. We used the N₂ stretching vibration as a reporter chromophore to estimate how electronic and steric effects affect the activation of the molecular nitrogen by these copper complexes. In contrast to the previous studies on nitrogen activation that probe “late activation” of the nitrogen molecule, our cryogenic studies give access to the “early activation” states that otherwise difficult to access. Our data show that the electronic character, as well as position and number of substituents, can affect the N-N vibrational frequency, leading either to a bigger or to a lesser degree of N₂ activation. Figure

Carbanions are highly reactive intermediates that are commonly used in organic synthesis. Here, we investigate the fundamental gas phase spectroscopy and isomerization of substituted aromatic phenides (deprotonated benzene derivatives) using isomer-selective cryogenic ion vibrational predissociation spectroscopy (1000 cm⁻¹– 4200 cm⁻¹). The phenide is formed by the decarboxylation of the 4-benzoyl benzoate anion (4BBA^–, C14H9O3^–), a substituted benzophenone, in a commercial Orbitrap mass spectrometer before being transferred to the triple focusing time-of-flight photofragmentation mass spectrometer. The resulting spectra are congested, suggesting the presence of multiple isomers. They are revealed by quantum chemical calculations in conjunction with two color IR-IR photobleaching spectroscopy to be the expected phenide, and a new molecule formed by multiple steps of isomerization that end in ring-closed product. The identities of these compounds and the proposed mechanism are confirmed by additional experiments using 4BBA^–-d₉ and 2BBA^–.

Ethylenediaminetetraacetic acid (EDTA) can be used as a chelating agent for binding metal ions in solution. In addition, its binding pocket is a model for the interactions between carboxylate groups and the divalent ions they often bind in some biological systems.S. Mitra, K. Werling, E. Berquist, D. S. Lambrecht, S. Garrett-Roe, J. Phys. Chem. A 125 (2021) 4867-4881S. C. Edington, C. R. Baiz, J. Phys. Chem. A 122 (2018) 6585-6592Q. Yuan, X. T. Kong, G. L. Hou, L. Jiang, X. B. Wang, Faraday Discuss. 217 (2019) 383ith its four carboxyl groups and two nitrogen atoms, EDTA can chelate nearly any metal cation to form water-soluble complexes, making it a robust model system for studying biologically relevant divalent ion-carboxylate interactions. Here, we present cryogenic gas-phase infrared spectra of a series of alkaline earth metal-EDTA complexes of the form [M(II)·EDTA]²⁻ and assign spectral features using density functional theory calculations. The vibrational spectra encode structural and electrostatic information, reflecting the geometry of each metal ion within the EDTA binding pocket and its relation to ionic radius. S. Mitra, K. Werling, E. Berquist, D. S. Lambrecht, S. Garrett-Roe, J. Phys. Chem. A 125 (2021) 4867-4881

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Footnotes:

Q. Yuan, X. T. Kong, G. L. Hou, L. Jiang, X. B. Wang, Faraday Discuss. 217 (2019) 383W

The cyanate anion NCO^- is a species of considerable astrophysical relevance. It is widely believed to be embedded in interstellar ices present in young stellar objects but has not yet been detected in the dense gas of the interstellar medium. Here, very accurate laboratory measurements of the rotational spectrum of the N¹³CO^- isotopologue at submillimeter wavelengths and three additional lines of the parent isotopologue up to 437.4 GHz are reported. With this new data, the rotational spectrum of both isotopologues can be predicted to better 0.25 km s⁻¹ in equivalent radial velocity up to 1 THz. Moreover, a semiexperimental equilibrium structure of the anion is derived by combining the experimental ground-state rotational constants of the two isotopologues with theoretical vibrational corrections, obtained by using the coupled-cluster method with inclusion of single and double excitations and perturbative inclusion of triple excitations (CCSD(T)). The estimated accuracy of the two bond distances is on the order of 5×10⁻⁴ Å.