More Like this

1. The bismuth tetramer Bi ₄ : the ν ₃ key to experimental observation

   https://doi.org/10.1039/C8CP03529F  

   Lahm, Mitchell E.; Hoobler, Preston R.; Turney, Justin M.; Peterson, Kirk A.; Schaefer, Henry F. (January 2018, Physical Chemistry Chemical Physics)

   The spectroscopic identification of Bi 4 has been very elusive. Two constitutional Bi 4 isomers of T d and C 2v symmetry are investigated and each is found to be a local energetic minimum. The optimized geometries and vibrational frequencies of these two isomers are obtained at the CCSD(T)/cc-pVQZ-PP level of theory, utilizing the Stoll, Metz, and Dolg 60-electron effective core potential. The fundamental frequencies of the T d isomer are obtained at the same level of theory. The focal point analysis method, from a maximum basis set of cc-pV5Z-PP, and proceeding to a maximum correlation method of CCSDTQ, was employed to determine the dissociation energy of Bi 4 ( T d ) into two Bi 2 and the adiabatic energy difference between the C 2v and T d isomers of Bi 4 . These quantities are predicted to be +65 kcal mol −1 and +39 kcal mol −1 , respectively. Two electron vertical excitation energies between the T d and C 2v electronic configurations are computed to be 156 kcal mol −1 for the T d isomer and 9 kcal mol −1 for the C 2v isomer. The most probable approach to laboratory spectroscopic identification of Bi 4 is via an infrared spectrum. The predicted fundamentals (cm −1 ) with harmonic IR intensities in parentheses (km mol −1 ) are 94(0), 123(0.23), and 167(0) for the T d isomer. The moderate IR intensity for the only allowed fundamental may explain why Bi 4 has yet to be observed. Through natural bond orbital analysis, the C 2v isomer of Bi 4 was discovered to exhibit “long-bonding” between the furthest apart ‘wing’ atoms. This long-bonding is postulated to be facilitated by the σ-bonding orbital between the ‘spine’ atoms of the C 2v isomer. 

   more » « less
2. Nonadiabatic coupling of the dynamical structure to the superconductivity in YSr ₂ Cu _2.75 Mo _0.25 O _7.54 and Sr ₂ CuO _3.3

   https://doi.org/10.1073/pnas.2018336117  

   Conradson, Steven D.; Geballe, Theodore H.; Jin, Chang-Qing; Cao, Li-Peng; Gauzzi, Andrea; Karppinen, Maarit; Baldinozzi, Gianguido; Li, Wen-Min; Gilioli, Edmondo; Jiang, Jack M.; et al (December 2020, Proceedings of the National Academy of Sciences)

   null (Ed.)

   A crucial issue in cuprates is the extent and mechanism of the coupling of the lattice to the electrons and the superconductivity. Here we report Cu K edge extended X-ray absorption fine structure measurements elucidating the internal quantum tunneling polaron (iqtp) component of the dynamical structure in two heavily overdoped superconducting cuprate compounds, tetragonal YSr 2 Cu 2.75 Mo 0.25 O 7.54 with superconducting critical temperature, T c = 84 K and hole density p = 0.3 to 0.5 per planar Cu, and the tetragonal phase of Sr 2 CuO 3.3 with T c = 95 K and p = 0.6. In YSr 2 Cu 2.75 Mo 0.25 O 7.54 changes in the Cu-apical O two-site distribution reflect a sequential renormalization of the double-well potential of this site beginning at T c , with the energy difference between the two minima increasing by ∼6 meV between T c and 52 K. Sr 2 CuO 3.3 undergoes a radically larger transformation at T c , >1-Å displacements of the apical O atoms. The principal feature of the dynamical structure underlying these transformations is the strongly anharmonic oscillation of the apical O atoms in a double-well potential that results in the observation of two distinct O sites whose Cu–O distances indicate different bonding modes and valence-charge distributions. The coupling of the superconductivity to the iqtp that originates in this nonadiabatic coupling between the electrons and lattice demonstrates an important role for the dynamical structure whereby pairing occurs even in a system where displacements of the atoms that are part of the transition are sufficiently large to alter the Fermi surface. The synchronization and dynamic coherence of the iqtps resulting from the strong interactions within a crystal would be expected to influence this process. 

   more » « less
3. Preparation of methanediamine (CH ₂ (NH ₂ ) ₂ )—A precursor to nucleobases in the interstellar medium

   https://doi.org/10.1073/pnas.2217329119  

   Marks, Joshua H.; Wang, Jia; Fortenberry, Ryan C.; Kaiser, Ralf I. (December 2022, Proceedings of the National Academy of Sciences)

   Although methanediamine (CH 2 (NH 2 ) 2 ) has historically been the subject of theoretical scrutiny, it has never been isolated to date. Here, we report the preparation of methanediamine (CH 2 (NH 2 ) 2 )—the simplest diamine. Low-temperature interstellar analog ices composed of ammonia and methylamine were exposed to energetic electrons which act as proxies for secondary electrons produced in the track of galactic cosmic rays. These experimental conditions, which simulate the conditions within cold molecular clouds, result in radical formation and initiate aminomethyl (ĊH 2 NH 2 ) and amino ( N . H 2 ) radical chemistry. Exploiting tunable photoionization reflectron time-of-flight mass spectrometry (PI-ReToF-MS) to make isomer-specific assignments, methanediamine was identified in the gas phase upon sublimation, while its isomer methylhydrazine (CH 3 NHNH 2 ) was not observed. The molecular formula was confirmed to be CH 6 N 2 through the use of isotopically labeled reactants. Methanediamine is the simplest molecule to contain the NCN moiety and could be a vital intermediate in the abiotic formation of heterocyclic and aromatic systems such as nucleobases, which all contain the NCN moiety. 

   more » « less
4. The use of DOSY experiments to determine the solution structures of coinage metal pyrazolates: The case of {[3,5‐(CF ₃ ) ₂ Pz]Ag} ₃

   https://doi.org/10.1002/mrc.5242  

   Alkorta, Ibon; Benito, María_Teresa; Elguero, José; Doyagüez, Elisa_García; Patterson, Monika_R; Jimeno, María_Luisa; Dias, H_V_Rasika; Reviriego, Felipe (January 2022, Magnetic Resonance in Chemistry)

   Abstract A series of DOSY experiments have been carried out to determine the solution stoichiometry of silver(I) 3,5‐bis (trifluoromethyl)pyrazolate species. This compound exists as a trimer in the solid state (n = 3) but in solutions of chlorinated solvents, the DOSY data suggest the presence of a mixture of solvent stabilized monomer (n = 1) and dimer (n = 2) in equilibrium. Different approximations have been used including the Stokes–Einstein and the Stokes–Einstein–Gierer–Wirtz equations. Some methodological problems are discussed. 

   more » « less
5. The distance to the Serpens South cluster from H ₂ O masers

   https://doi.org/10.1051/0004-6361/202346369  

   Ortiz-León, Gisela N.; Dzib, Sergio A.; Loinard, Laurent; Gong, Yan; Pillai, Thushara; Plunkett, Adele (May 2023, Astronomy & Astrophysics)

   In this Letter we report Very Long Baseline Array observations of 22 GHz water masers toward the protostar CARMA–6 , located at the center of the Serpens South young cluster. From the astrometric fits to maser spots, we derive a distance of 440.7±3.5 pc for the protostar (1% error). This represents the best direct distance determination obtained so far for an object this young and deeply embedded in this highly obscured region. Taking depth effects into account, we obtain a distance to the cluster of 440.7 ± 4.6 pc. Stars visible in the optical that have astrometric solutions in the Gaia Data Release 3 are, on the other hand, all located at the periphery of the cluster. Their mean distance of 437 −41 +51 pc is consistent within 1 σ with the value derived from maser astrometry. As the maser source is at the center of Serpens South, we finally solve the ambiguity of the distance to this region that has prevailed over the years. 

   more » « less