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1. Fine-structure transitions of Si and S induced by collisions with atomic hydrogen

   https://doi.org/10.1093/mnras/stad1050  

   Yan, Pei-Gen; Babb, James F (April 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Using a quantum-mechanical close-coupling method, we calculate cross-sections for fine-structure excitation and relaxation of Si and S atoms in collisions with atomic hydrogen. Rate coefficients are calculated over a range of temperatures for astrophysical applications. We determine the temperature-dependent critical densities for the relaxation of Si and S in collisions with H and compare these to the critical densities for collisions with electrons. The present calculations should be useful in modelling environments exhibiting the [S i] 25 μm and [S i] 57 μm far-infrared emission lines or where cooling of S and Si by collisions with H is of interest. 

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2. Fine Tuning Electronic Structure of Catalysts through Atomic Engineering for Enhanced Hydrogen Evolution

   Huang, Y.C.; Hu, J.; Xu, H. X.; Bian, W.; Ge, J. X.; Zang, D. J.; Cheng, D.J.*; Lv, Y. K. (October 2018, Advanced energy materials)

   An efficient, durable, and low‐cost hydrogen evolution reaction (HER) catalyst is an essential requirement for practical hydrogen production. Herein, an effective approach to facilitate the HER kinetics of molybdenum carbide (Mo2C) electrocatalysts is presented by tuning its electronic structure through atomic engineering of nitrogen implantation. Starting from the organoimido‐derivatized polyoxometalate nanoclusters with inherent Mo-N bonds, the formation of N‐implanted Mo2C (N@Mo2C) nanocrystals with perfectly adjustable amounts of N atoms is demonstrated. The optimized N@Mo2C electrocatalyst exhibits remarkable HER performance and good stability over 20 h in both acid and basic electrolytes. Further density functional theory calculations show that engineering suitable nitrogen atoms into Mo2C can regulate its electronic structure well and decrease Mo-H strength, leading to a great enhancement. 

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3. Fine-structure Excitation of O( ³ P) Induced by Collisions with Atomic Hydrogen

   https://doi.org/10.3847/2515-5172/ac81cf  

   Yan, Pei-Gen; Babb, James F. (July 2022, Research Notes of the AAS)

   Abstract The utility of the far-infrared lines of oxygen as diagnostics of gas outflows and for other applications depends on accurate descriptions of the rate coefficients for excitation (and relaxation) through collisions with electrons and with hydrogen atoms. For O and H collisions, earlier calculations of rate coefficients show discrepancies leading to ambiguity in astrophysical applications. In this note we introduce a methodology that yields consistent sets of rate coefficients for a number of cases. We then apply our method to the O–H system in order to investigate the discrepancies. The present rate coefficients will be of particular interest for modeling observations of astrophysical environments in the far-infrared. 

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4. Constraining Lyman-alpha spatial offsets at 3 < z < 5.5 from VANDELS slit spectroscopy

   https://doi.org/10.1093/mnras/stz1768  

   Hoag, A; Treu, T; Pentericci, L; Amorin, R; Bolzonella, M; Bradač, M; Castellano, M; Cullen, F; Fynbo, J P; Garilli, B; et al (July 2019, Monthly Notices of the Royal Astronomical Society)

   Abstract We constrain the distribution of spatially offset Lyman-alpha emission (Ly α) relative to rest-frame ultraviolet emission in ∼300 high redshift (3 < z < 5.5) Lyman-break galaxies (LBGs) exhibiting Ly α emission from VANDELS, a VLT/VIMOS slit-spectroscopic survey of the CANDELS Ultra Deep Survey and Chandra Deep Field South fields (≃0.2 deg2 total). Because slit spectroscopy only provides one spatial dimension, we use Bayesian inference to recover the underlying two-dimensional Ly α spatial offset distribution. We model the distribution using a two-dimensional circular Gaussian, defined by a single parameter σr,Ly α, the standard deviation expressed in polar coordinates. Over the entire redshift range of our sample (3 < z < 5.5), we find $$\sigma _{r,\mathrm{Ly}\,\alpha }=1.70^{+0.09}_{-0.08}$$ kpc ($$68\hbox{ per cent}$$ conf.), corresponding to ∼0$${^{\prime\prime}_{.}}$$25 at 〈z〉 = 4.5. We also find that σr,Ly α decreases significantly with redshift. Because Ly α spatial offsets can cause slit losses, the decrease in σr,Ly α with redshift can partially explain the increase in the fraction of Ly α emitters observed in the literature over this same interval, although uncertainties are still too large to reach a strong conclusion. If σr,Ly α continues to decrease into the reionization epoch, then the decrease in Ly α transmission from galaxies observed during this epoch might require an even higher neutral hydrogen fraction than what is currently inferred. Conversely, if spatial offsets increase with the increasing opacity of the intergalactic medium, slit losses may explain some of the drop in Ly α transmission observed at z > 6. Spatially resolved observations of Ly α and UV continuum at 6 < z < 8 are needed to settle the issue. 

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5. Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N ii] Fine-structure and Hydrogen Recombination Lines

   https://doi.org/10.3847/1538-4357/ab46c2  

   Pineda, Jorge L.; Horiuchi, Shinji; Anderson, Loren D.; Luisi, Matteo; Langer, William D.; Goldsmith, Paul F.; Kuiper, Thomas B.; Bryden, Geoff; Soriano, Melissa; W. Lazio, T. Joseph (November 2019, The Astrophysical Journal)