In order to improve transition metal catalyst performance, we must first understand the mechanistic features and intermediates in these reactions. Despite great progress in the field, some intermediates can be particularly hard to isolate and investigate. These difficulties can be overcome by forming these intermediates in the gas-phase. Specifically, collision induced dissociation of a precursor creates a vacant ligand position in the precursor which allows for a facile ion-molecule reaction in an ion trap to produce the desired intermediate. These intermediates can then be captured by evaporative quenching of collision complexes and their structures can be probed via cryogenic ion vibrational spectroscopy. In this work, we utilize these gas-phase techniques to focus on two transition metal catalyst systems: a [Ru^II(bpy)(tpy)(H₂O)]²⁺ water oxidation catalyst as well as two (N-N)PtCl₂ catalysts (N-N= ethylene diamine (en), diamine (NH₃)₂) for C-H activation and functionalization. For the ruthenium water oxidation catalyst, we have formed the elusive oxo intermediate by reacting [Ru(bpy)(tpy)]²⁺ with O₃ to readily produce [Ru(bpy)(tpy)O]²⁺. Interestingly, since the oxo readily forms with ozone but does not with N₂O, this indicates that the spin state of the Ru=O is a triplet. This structure is confirmed by the observation of the Ru=O vibration. For the (N-N)PtCl₂ catalysts, we prepare the sigma-CH intermediates by reacting [(N-N)PtCl]¹⁺ with various alkanes and alkenes such as methane and benzene.

The millimeter/submillimeter spectrum of magnesium chloride (MgCl) has been measured in an electronic excited state, using direct absorption spectroscopy in the range of 240-310 GHz. The molecule was synthesized by reacting chlorine gas (Cl₂) with magnesium vapor, produced using a Broida-type oven in the presence of argon carrier gas. Seven rotational transitions in each of six isotopologues (²⁴Mg³⁵Cl, ²⁴Mg³⁷Cl, ²⁵Mg³⁵Cl, ²⁵Mg³⁷Cl, ²⁶Mg³⁵Cl, ²⁶Mg³⁷Cl) were measured in the ground vibrational state, with a number of vibrationally excited satellite lines (v=1-4) also being observed for each species. From the data, rotational, fine structure, and ²⁵Mg hyperfine (²⁵MgCl only) parameters were determined for the six isotopologues in this state, as well as equilibrium constants and the equilibrium bond length, r_e = 2.54 Å. Based on theoretical calculations, this excited state has been identified as (2)²Π_i, which has never before been observed experimentally. The excited state manifold of MgCl has been the subject of a number of computational studies, and is of interest for laser cooling experiments.

Electrocatalytic reduction of CO₂ into feedstock for chemical fuels is a promising approach to achieving a carbon neutral fuel cycle.M. M. Foreman, R. J. Hirsch, J. M. Weber, J. Phys. Chem. A 125 (2021) 7297-7302hile this has been an active field of study for decades, relatively little is known about the key reaction intermediates and molecular-level processes of proposed catalytic mechanisms, necessitating a deeper understanding to inform the design of future catalysts. We present cryogenic gas-phase infrared spectra of catalytically relevant model systems consisting of a transition metal center (Co, Ni, or Cu) coordinated to two bipyridine-based ligands, either bare or with a formate adduct.E. E. Benson, C. P. Kubiak, A. J. Sathrum, J. M. Smieja, Chem. Soc. Rev. 38 (2009) 89–99ipyridine derivatives are frequently ligands for molecular catalysts where a transition metal ion is coordinated to four N atoms. This family of metal-4N catalysts has been studied extensively due to their exceptional performance and ease of synthesis. Formate is one of many possible CO₂ reduction products.J. M. Savéant Chem. Rev. 108 (2008) 2348–2378T. Shimoda, T. Morishima, K. Kodama, T. Hirose, D. E. Polyansky, G. F. Manbeck, J. T. Mucherman, E. Fujita, Inorg. Chem. 57 (2018) 5486-5498 Density functional theory was used to assign spectral features and calculate charge distributions. The vibrational spectra inform us of the structure of and intermolecular forces in each complex, revealing the binding motif of the formate adduct to the metal center and the dependence of this arrangement on the identity of the metal. The calculated charge distributions demonstrate the role of the organic ligands to act as charge reservoirs, where they show remarkable electronic flexibility in response to the addition of a formate adduct and the nature of the coordinated metal center. This work showcases the influence of transition metal identity on the formate-metal binding motif and the significant role of the organic ligand framework in adjusting the redox properties of these complexes.

---

Footnotes:

M. M. Foreman, R. J. Hirsch, J. M. Weber, J. Phys. Chem. A 125 (2021) 7297-7302W E. E. Benson, C. P. Kubiak, A. J. Sathrum, J. M. Smieja, Chem. Soc. Rev. 38 (2009) 89–99B J. M. Savéant Chem. Rev. 108 (2008) 2348–2378

---

Footnotes:

At the 2021 ISMS conference, we presented a talk on the high resolution spectroscopy of the RuO molecule.A.G. Adam, G.M. Chenard, C. Linton, and D.W. Tokaryk, http://hdl.handle.net/2142/111251.his talk was primarily about the observation of the seven isotopologues of ⁿRuO (n= 104, 102, 101, 100, 99, 98, and 96) plus hyperfine structure resolved in the ¹⁰¹RuO and ⁹⁹RuO isotopologues of the 2-0, 1-0, and 0-0 bands of the green [18.1]4 – X⁵∆₄ and [18.1]3 – X⁵∆₃ electronic transitions. Comparison was made to the earlier work of Wang et al.N. Wang, Y.W. Ng, and A.S.-C. Cheung, J. Phys. Chem. A, 117, 13279-13283, (2013).e mentioned that future work would centre on the high resolution spectroscopy of the red [16.0]5 - X⁵∆₄ electronic system. We will now report on the 2-0, 1-0, and 0-0 bands of this system plus our assignments of other spin-orbit transitions associated with this red system. The work has yielded the isotopologues listed above as well as resolved hyperfine structure for the ¹⁰¹RuO and ⁹⁹RuO isotopologues. The observation of the extra spin-orbit transitions gives us the spin-orbit intervals for the ground and excited states. Results of our hyperfine analysis will be used to discuss the electronic configurations associated with both the red and the green electronic transitions.

---

Footnotes:

A.G. Adam, G.M. Chenard, C. Linton, and D.W. Tokaryk, http://hdl.handle.net/2142/111251.T N. Wang, Y.W. Ng, and A.S.-C. Cheung, J. Phys. Chem. A, 117, 13279-13283, (2013).W

We present our investigations of the magnetic response of A⁶Σ⁺- X ⁶Σ⁺ transitions in CrH, in fields up to 0.5 Tesla, focusing on the strong dissymmetry between σ⁺ and σ⁻ transitions, observed as predictedKuzmychov and Berdyugina, Astron. Astrophys. 558, A120 (2013)t modest magnetic field strengths. This dissymmetry is recorded as Stokes V signals in telescope spectropolarimetry, where it gives a sensitive probe of stellar magnetism. CrH (and FeH) bands feature prominently in spectra of cool dwarf stars taken for example on the SPIRou spectropolarimeter (searching for exoplanets at the Canada-France-Hawaii telescope). Ultimately, our work should help to discriminate effects of stellar magnetism from exoplanet presence in radial velocity data derived from telescope spectropolarimetric measurements. Field-free line positions are well-documentedBauschlicher et al., J. Chem. Phys. 115, 1312 (2001); Ram et al., J. Mol. Spectrosc. 161 445 (1993);

 Chowdhury et al., Phys. Chem. Chem. Phys. 8, 822 (2006); Kleman and Uhler, Can. J. Phys 37 537 (1959)or the 760 and 870 nm bands of the A-X system. IR laser magnetic resonance studiesLipus et al., Mol. Phys. 73 (5), 1041 (1991)rovide some ground state Landé factors, but the Zeeman effect has been investigated for only the lowest rotational levels of the A state, under molecular beam conditionsChen et al., Phys. Chem. Chem. Phys. 8, 822 (2006). To extend these observations, we have recorded cavity-enhanced absorption data (providing relative intensities in zero field conditions) and laser-induced fluorescence spectra using circularly polarised light, with a discharge source producing CrH at around 500 K.

---

Footnotes:

Kuzmychov and Berdyugina, Astron. Astrophys. 558, A120 (2013)a Bauschlicher et al., J. Chem. Phys. 115, 1312 (2001); Ram et al., J. Mol. Spectrosc. 161 445 (1993);

 Chowdhury et al., Phys. Chem. Chem. Phys. 8, 822 (2006); Kleman and Uhler, Can. J. Phys 37 537 (1959)f Lipus et al., Mol. Phys. 73 (5), 1041 (1991)p Chen et al., Phys. Chem. Chem. Phys. 8, 822 (2006)..

Calcium monohydride CaH is an astronomical molecule identified in the Sun and other stars by using the visible transitions. We have found many new vibrational levels of the A²Π, B/B′²Σ⁺, and 1²∆ state using laser induced fluorescence (LIF) from visible to ultraviolet region. K. Watanabe, N. Yoneyama, K. Uchida, K. Kobayashi, F. Matsushima, Y. Moriwaki, S. C. Ross, Chem. Phys. Lett. 657, 1 (2016).^, K. Watanabe, I. Tani, K. Kobayashi, Y. Moriwaki, S. C. Ross, Chem. Phys. Lett. 710, 11 (2018).J. Furuta, K. Watanabe, I. Tani, K. Kobayashi, Y. Moriwaki, S. C. Ross, International Symposium on Molecular Spectroscopy, 74th meeting, TI06, (2019). S. Yaguramaki, J. Furuta, I. Tani, K. Kobayashi, Y. Moriwaki, S. C. Ross, The 2021 International Symposium on Molecular Spectroscopy, WM11, (2021).he pure rotational spectra of the ground state have been measured and analyzed, including the hyperfine structure. C. I. Frum, J. J. Oh, E. A. Cohen, H. M. Pickett, Astrophys. J. Lett. 408, L61 (1993).^,W. L. Barclay Jr., M. A. Anderson, L. M. Ziurys, Astrophys. J. Lett. 408, L65 (1993).owever, the N range was limited to N = 2−1 and the highest frequency was about 500 GHz. In this study, we will report our new measurement in the terahertz region. The terahertz spectra were taken by using tunable far-infrared spectrometer at University of Toyama. Calcium monohydride was produced in a quartz cell where Ca vapor was introduced by heating Ca at 750^°C and DC discharge was applied under H₂ and He (or Ar) gas environment. The highest frequencies of the ground state and vibrationally excited state are approximately 3.7 THz and 1.9 THz, respectively.

---

Footnotes:

K. Watanabe, N. Yoneyama, K. Uchida, K. Kobayashi, F. Matsushima, Y. Moriwaki, S. C. Ross, Chem. Phys. Lett. 657, 1 (2016). \end K. Watanabe, I. Tani, K. Kobayashi, Y. Moriwaki, S. C. Ross, Chem. Phys. Lett. 710, 11 (2018).\end

---

Footnotes:

S. Yaguramaki, J. Furuta, I. Tani, K. Kobayashi, Y. Moriwaki, S. C. Ross, The 2021 International Symposium on Molecular Spectroscopy, WM11, (2021).T\end C. I. Frum, J. J. Oh, E. A. Cohen, H. M. Pickett, Astrophys. J. Lett. 408, L61 (1993). W. L. Barclay Jr., M. A. Anderson, L. M. Ziurys, Astrophys. J. Lett. 408, L65 (1993).H

Transition metal nitrides are of growing interest due to their catalytic, energy storage, sensing, superconducting, and mechanical properties. The (0,0) band of the A ⁴Π_r – X ⁴Σ⁻ transition of MoN was recorded at Doppler-limited resolution using intracavity laser spectroscopy (ILS) integrated with a Fourier-transform spectrometer used for detection (ILS-FTS). The target MoN molecules were produced in the plasma discharge of a molybdenum-lined copper hollow cathode, using a gas mixture of Ar with about 1% N₂ in a reaction chamber with about 1 Torr total pressure. Isotopologue structure in the spectrum is clearly visible and analysis is underway for the five abundant isotopologues with no nuclear spin (I_Mo=0): ⁹²MoN (14.6%), ⁹⁴MoN (9.2%), ⁹⁶MoN (16.7%), ⁹⁸MoN (24.3%), and ¹⁰⁰MoN (9.7%). The progress, preliminary results of this analysis, and comparison to a recent high-level computational study will be provided.

The complex electronic structure of transition metal diatomic molecules, such as tungsten monosulfide (WS), makes them intriguing targets for high level spectroscopic analysis. A plethora of electrons and accessible valence orbitals make WS a difficult molecule to model computationally due to the large number of possible electronic interactions. The (0,0) and (1,0) vibrational bands of the [15.30]1 – X ³Σ⁻(0⁺) transition of WS were recorded in absorption at Doppler-limited resolution using intracavity laser spectroscopy integrated with a Fourier-transform spectrometer used for detection (ILS-FTS). The target WS molecules were produced in the plasma discharge of a tungsten-lined copper hollow cathode, using a gas mixture of approximately 70% Ar and 30% H₂, with a trace amount of CS₂, giving a reaction chamber pressure of about 1 torr total. Within each spectrum, evidence of heterogeneous mass- and J-dependent perturbations were observed across all four abundant isotopologues: ¹⁸²W³²S, ¹⁸³W³²S, ¹⁸⁴W³²S, and ¹⁸⁶W³²S. The perturbations observed in the (0,0) and (1,0) bands were attributed to interactions with lines in the v=2 and v=3 vibrational levels of the [14.26]0⁺ state of WS. Rotational and deperturbation analyses incorporated a mass-independent Dunham model built into PGOPHER to fit lines from the two [15.30]1 transition bands, as well as line positions from several bands of the [14.26]0⁺ – X ³Σ⁻(0⁺) transition previously analyzed by our group (J.C. Harms et al., J. Mol. Spec. 2020 (374), 111378). The results of this analysis and comparison with previous computational work (J. Zhang et al., J. Quant. Spectrosc. Radiat. Transfer. 2020 (256), 107314) will be presented.

The chemi-ionization reactions of atomic lanthanides M+O → MO⁺ + e⁻ are currently being investigated as a method to artificially increase the localized electron density in the ionosphere for uniform radio wave propagation. Recent experiments involving the release of atomic samarium (Sm) into the upper atmosphere have resulted in the production of a cloud with blue and red emissions[1]. Spectroscopic characterization of SmO is required to accurately determine the fraction of SmO present in the release cloud. While the low-lying states of SmO have been previously spectroscopically characterized, the analysis was hindered due to the production of SmO under high temperature conditions[2,3]. In this work, jet-cooled SmO was produced and low- and high-resolution laser-induced fluorescence (LIF) as well as dispersed laser-induced fluorescence (DLIF) techniques were employed for electronic structure characterization. For the first time, vibrational constants for several low-lying states have been determined. Using high-resolution LIF, the hyperfine structure of the (1)1 v = 0 and [15.35]1 v = 0,1 states was recorded. Data and analysis of ground and low-lying excited states of SmO will be presented.
[1] Ard, S.G. et al. J. Chem. Phys.2015, 143, 204303. [2] Hannigan, M. C. J. Mol. Spec. 1983, 99, 235-238. [3] Linton, C. et al. J. Mol. Spec. 1987, 126, 370-392.