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1. Diruthenium aryl compounds – tuning of electrochemical responses and solubility

   https://doi.org/10.1039/D1DT03957A  

   Miller-Clark, Lyndsy A.; Christ, Peter E.; Ren, Tong (January 2022, Dalton Transactions)

   Reported herein are the two new series of diruthenium aryl compounds: Ru 2 (DiMeOap) 4 (Ar) (1a–6a) (DiMeOap = 2-(3,5-dimethoxyanilino)pyridinate) and Ru 2 ( m - i PrOap) 4 (Ar) (1b–5b) ( m - i PrOap = 2-(3-iso-propoxyanilino)pyridinate), prepared through the lithium-halogen exchange reaction with a variety of aryl halides (Ar = C 6 H 4 -4-NMe 2 (1), C 6 H 4 -4- t Bu (2), C 6 H 4 -4-OMe (3), C 6 H 3 -3,5-(OMe) 2 (4), C 6 H 4 -4-CF 3 (5), C 6 H 5 (6)). The molecular structures of these compounds were established with X-ray diffraction studies. Additionally, these compounds were characterized using electronic absorption and voltammetric techniques. Compounds 1a–6a and 1b–5b are all in the Ru 2 5+ oxidation state, with a ground state configuration of σ 2 π 4 δ 2 (π*δ*) 3 ( S = 3/2). Use of the modified ap ligands (ap′) resulted in moderate increases of product yield when compared to the unsubstituted Ru 2 (ap) 4 (Ar) (ap = 2-anilinopyridinate) series. Comparisons of the electrochemical properties of 1a–6a and 1b–5b against the Ru 2 (ap′)Cl starting material reveals the addition of the aryl ligand cathodically shifted the Ru 2 6+/5+ oxidation and Ru 2 5+/4+ reduction potentials. These oxidation and reductions potentials are also strongly dependent on the p -substituent of the axial aryl ligands. 

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2. First detection and analysis of an electronic spectrum of vanadium hydride: The D ⁵ Π –X ⁵ Δ (0,0) band

   https://doi.org/10.1063/5.0105844  

   Varberg, Thomas D. (August 2022, The Journal of Chemical Physics)

   The D 5 Π–X 5 Δ (0,0) band of vanadium hydride at 654 nm has been recorded by laser excitation spectroscopy and represents the first analyzed spectrum of VH in the gas phase. The molecules were generated using a hollow cathode discharge source, with laser-induced fluorescence detected via the D 5 Π–A 5 Π (0,0) transition. All five main (ΔΩ = ΔΛ) subbands were observed as well as several satellite ones, which together create a rather complex and overlapped spectrum covering the region 15 180–15 500 cm −1 . The D 5 Π state displays the effects of three strong local perturbations, which are likely caused by interactions with high vibrational levels of the B 5 Σ − and c 3 Σ − states, identified in a previous multiconfigurational self-consistent field study by Koseki et al. [J. Phys. Chem. A 108, 4707 (2004)]. Molecular constants describing the X 5 Δ, A 5 Π, and D 5 Π states were determined in three separate least-squares fits using effective Hamiltonians written in a Hund’s case (a) basis. The fine structure of the ground state is found to be consistent with its assignment as a σπ 2 δ, 5 Δ electronic state. The fitted values of its first-order spin–orbit and rotational constants in the ground state are [Formula: see text] and B = 5.7579(13) cm −1 , the latter of which yields a bond length of [Formula: see text] Å. This experimental value is in good agreement with previous computational studies of the molecule and fits well within the overall trend of decreasing bond length across the series of 3d transition metal monohydrides. 

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3. Laboratory Study of the Cameron Bands, the First Negative Bands, and Fourth Positive Bands in the Middle Ultraviolet 180–280 nm by Electron Impact Upon CO

   https://doi.org/10.1029/2020JE006602  

   Lee, Rena A.; Ajello, Joseph M.; Malone, Charles P.; Evans, J. Scott; Veibell, Victoir; Holsclaw, Gregory M.; McClintock, William E.; Hoskins, Alan C.; Jain, Sonal; Gérard, Jean‐Claude; et al (January 2021, Journal of Geophysical Research: Planets)

   Abstract We have analyzed medium‐resolution (full width at half maximum, FWHM = 1.2 nm), Middle UltraViolet (MUV; 180–280 nm) laboratory emission spectra of carbon monoxide (CO) excited by electron impact at 15, 20, 40, 50, and 100 eV under single‐scattering conditions at 300 K. The MUV emission spectra at 100 eV contain the Cameron Bands (CB) CO(a³Π → X¹Σ⁺), the fourth positive group (4PG) CO(A¹Π → X¹Σ⁺), and the first negative group (1NG) CO⁺(B²Σ⁺→ X²Σ) from direct excitation and cascading‐induced emission of an optically thin CO gas. We have determined vibrational intensities and emission cross sections for these systems, important for modeling UV observations of the atmospheres of Mars and Venus. We have also measured the CB “glow” profile about the electron beam of the long‐lived CO (a³Π) state and determined its average metastable lifetime of 3 ± 1 ms. Optically allowed cascading from a host of triplet states has been found to be the dominant excitation process contributing to the CB emission cross section at 15 eV, most strongly by the d³Δ and a'³Σ⁺electronic states. We normalized the CB emission cross section at 15 eV electron impact energy by multilinear regression (MLR) analysis to the blended 15 eV MUV spectrum over the spectral range of 180–280 nm, based on the 4PG emission cross section at 15 eV that we have previously measured (Ajello et al., 2019,https://doi.org/10.1029/2018ja026308). We find the CB total emission cross section at 15 eV to be 7.7 × 10⁻¹⁷ cm². 

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4. The dicarbon bonding puzzle viewed with photoelectron imaging

   https://doi.org/10.1038/s41467-019-13039-y  

   Laws, B. A.; Gibson, S. T.; Lewis, B. R.; Field, R. W. (December 2019, Nature Communications)

   null (Ed.)

   Abstract Bonding in the ground state of C $${}_{2}$$ 2 is still a matter of controversy, as reasonable arguments may be made for a dicarbon bond order of $$2$$ 2 , $$3$$ 3 , or $$4$$ 4 . Here we report on photoelectron spectra of the C $${}_{2}^{-}$$ 2 − anion, measured at a range of wavelengths using a high-resolution photoelectron imaging spectrometer, which reveal both the ground $${X}^{1}{\Sigma}_{\mathrm{g}}^{+}$$ X 1 Σ g + and first-excited $${a}^{3}{\Pi}_{{\mathrm{u}}}$$ a 3 Π u electronic states. These measurements yield electron angular anisotropies that identify the character of two orbitals: the diffuse detachment orbital of the anion and the highest occupied molecular orbital of the neutral. This work indicates that electron detachment occurs from predominantly $$s$$ s -like ( $$3{\sigma}_{\mathrm{g}}$$ 3 σ g ) and $$p$$ p -like ( $$1{\pi }_{{\mathrm{u}}}$$ 1 π u ) orbitals, respectively, which is inconsistent with the predictions required for the high bond-order models of strongly $$sp$$ s p -mixed orbitals. This result suggests that the dominant contribution to the dicarbon bonding involves a double-bonded configuration, with 2 $$\pi$$ π bonds and no accompanying $$\sigma$$ σ bond. 

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5. One-dimensional temperature measurement of supersonic jet flow by resonantly ionized photoemission thermometry of molecular nitrogen

   https://doi.org/10.1364/OPTCON.543309  

   Clark, Aleksander; McCord, Walker; Pride, Kyle; Zhang, Zhili (December 2024, Optics Continuum)

   As the field of fluid dynamics progresses, the demand for sophisticated diagnostic methods to accurately assess flow conditions rises. In this work, resonantly ionized photoemission thermometry (RIPT) has been used to directly target and ionize diatomic nitrogen (N₂) to measure one-dimensional (1D) temperature profiles in a supersonic jet flow. This technique can be considered non-intrusive as the premise uses resonantly enhanced multiphoton ionization (REMPI) to target molecular nitrogen. This resonance excites N₂into absorption bands of the P, Q, and R rotational branches of N₂(b¹Π_u). The ideal (3 + 1) REMPI scheme excites from the ground state and ionizes N₂(b¹Π_u←X¹Σ_g⁺) where de-excitation results in photoemission from the first negative band of ionizedN₂⁺(B²Σ_u⁺→X²Σ_g⁺) as nitrogen returns to the ground state. The resulting emission can be observed using an intensified camera, thus permitting inference of the rotational temperature of ground-state molecular nitrogen. A linearly regressive Boltzmann distribution is applied based on previous calibration data for this technique to quantify the temperature along the ionized line. This work applies this technique to a pure N₂supersonic jet in cross-flow and counter-flow orientations to demonstrate N₂RIPT’s applications in a supersonic flow. Temperature variations are observed at different locations downstream of the exit in cross-flow, and axisymmetric in counter-flow, to generate profiles characterizing the flow dynamics. Due to the collisional effects resulting from the number density of N₂at higher pressures, a (3 + 2) REMPI scheme is observed throughout this text. 

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