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1. Atomic Transition Probabilities for Ultraviolet and Optical Lines of Tm II *

   https://doi.org/10.3847/1538-4365/ad614f  

   Den_Hartog, E A; Voith, G T; Roederer, I U (August 2024, The Astrophysical Journal Supplement Series)

   Abstract We report new branching fraction measurements for 224 ultraviolet and optical transitions of Tm II. These transitions range in wavelength (wavenumber) from 2350 to 6417 Å (42,532–15,579 cm⁻¹) and originate in 13 odd-parity and 24 even-parity upper levels. Thirty-five of the 37 levels, accounting for 213 of the 224 transitions, are studied for the first time. Branching fractions are determined for two levels studied previously for comparison to earlier results. The levels studied for the first time are high lying, ranging in energy from 35,753 to 54,989 cm⁻¹. The branching fractions are determined from emission spectra from two different high-resolution spectrometers. These are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5% to 30%. Comparison is made to experimental and theoretical transition probabilities from the literature where such data exist. These new log(gf) values are used to derive an abundance from one previously unused Tmiiline in the UV spectrum of ther-process-enhanced metal-poor star HD 222925, and this abundance is consistent with previous determinations based on other Tmiilines. 

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2. Origin of the ²⁹ Si NMR chemical shift in R ₃ Si–X and relationship to the formation of silylium (R ₃ Si ⁺ ) ions

   https://doi.org/10.1039/D0DT02099K  

   Huynh, Winn; Conley, Matthew P. (November 2020, Dalton Transactions)

   null (Ed.)

   The origin in deshielding of 29 Si NMR chemical shifts in R 3 Si–X, where X = H, OMe, Cl, OTf, [CH 6 B 11 X 6 ], toluene, and O X (O X = surface oxygen), as well as i Pr 3 Si + and Mes 3 Si + were studied using DFT methods. At the M06-L/6-31G(d,p) level of theory the geometry optimized structures agree well with those obtained experimentally. The trends in 29 Si NMR chemical shift also reproduce experimental trends; i Pr 3 Si–H has the most shielded 29 Si NMR chemical shift and free i Pr 3 Si + or isolable Mes 3 Si + have the most deshielded 29 Si NMR chemical shift. Natural localized molecular orbital (NLMO) analysis of the contributions to paramagnetic shielding ( σ p ) in these compounds shows that Si–R (R = alkyl, H) bonding orbitals are the major contributors to deshielding in this series. The Si–R bonding orbitals are coupled to the empty p-orbital in i Pr 3 Si + or Mes 3 Si + , or to the orbital in R 3 Si–X. This trend also applies to surface bound R 3 Si–O X . This model also explains chemical shift trends in recently isolated t Bu 2 SiH 2 + , t BuSiH 2 + , and SiH 3 + that show more shielded 29 Si NMR signals than R 3 Si + species. There is no correlation between isotropic 29 Si NMR chemical shift and charge at silicon. 

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3. CECILIA: The Faint Emission Line Spectrum of z ∼ 2–3 Star-forming Galaxies

   https://doi.org/10.3847/2041-8213/ad07dc  

   Strom, Allison L.; Rudie, Gwen C.; Trainor, Ryan F.; Brammer, Gabriel B.; Maseda, Michael V.; Raptis, Menelaos; Rogers, Noah S.; Steidel, Charles C.; Chen 陈, Yuguang 昱光; Law, David R. (November 2023, The Astrophysical Journal Letters)

   Abstract We present the first results from Chemical Evolution Constrained Using Ionized Lines in Interstellar Aurorae (CECILIA), a Cycle 1 JWST NIRSpec/MSA program that uses ultra-deep ∼30 hr G235M/F170LP observations to target multiple electron temperature-sensitive auroral lines in the spectra of 33 galaxies atz∼ 1–3. Using a subset of 23 galaxies, we construct two ∼600 object-hour composite spectra, both with and without the stellar continuum, and use these to investigate the characteristic rest-optical (λ_rest≈ 5700–8500 Å) spectrum of star-forming galaxies at the peak epoch of cosmic star formation. Emission lines of eight different elements (H, He, N, O, Si, S, Ar, and Ni) are detected, with most of these features observed to be ≲3% the strength of Hα. We report the characteristic strength of three auroral features ([Nii]λ5756, [Siii]λ6313, and [Oii]λλ7322, 7332), as well as other semi-strong and faint emission lines, including forbidden [Niii]λλ7380, 7414 and permitted Oiλ8449, some of which have never before been observed outside of the local Universe. Using these measurements, we findT_e[Nii] = 13,630 ± 2540 K, representing the first measurement of electron temperature using [Nii] in the high-redshift Universe. We also see evidence for broad line emission with a FWHM of ${536}_{-167}^{+45}$km s⁻¹; the broad component of Hαis 6.01%–28.31% the strength of the narrow component and likely arises from star-formation-driven outflows. Finally, we briefly comment on the feasibility of obtaining large samples of faint emission lines using JWST in the future. 

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4. The millimeter-wave spectrum of the SiP radical (X ² Π _i ): Rotational perturbations and hyperfine structure

   https://doi.org/10.1063/5.0118939  

   Burton, M. A.; Sheridan, P. M.; Ziurys, L. M. (November 2022, The Journal of Chemical Physics)

   The millimeter/submillimeter-wave spectrum of the SiP radical (X 2 Π i ) has been recorded using direct absorption spectroscopy in the frequency range of 151–532 GHz. SiP was synthesized in an AC discharge from the reaction of SiH 4 and gas-phase phosphorus, in argon carrier gas. Both spin–orbit ladders were observed. Fifteen rotational transitions were measured originating in the Ω = 3/2 ladder, and twelve in the Ω = 1/2 substate, each exhibiting lambda doubling and, at lower frequencies, hyperfine interactions from the phosphorus nuclear spin of I = 1/2. The lambda-doublets in the Ω = 1/2 levels appeared to be perturbed at higher J, with the f component deviating from the predicted pattern, likely due to interactions with the nearby excited A 2 Σ + electronic state, where ΔE Π-Σ ∼ 430 cm −1 . The data were analyzed using a Hund’s case a β Hamiltonian and rotational, spin–orbit, lambda-doubling, and hyperfine parameters were determined. A 2 Π/ 2 Σ deperturbation analysis was also performed, considering spin–orbit, spin-electronic, and L-uncoupling interactions. Although SiP is clearly not a hydride, the deperturbed parameters derived suggest that the pure precession hypothesis may be useful in assessing the 2 Π/ 2 Σ interaction. Interpretation of the Fermi contact term, b F , the spin-dipolar constant, c, and the nuclear spin-orbital parameter, a, indicates that the orbital of the unpaired electron is chiefly p π in character. The bond length in the v = 0 level was found to be r 0 = 2.076 Å, suggestive of a double bond between the silicon and phosphorus atoms. 

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5. Thermochemical studies of reactions of Re ⁺ with SO ₂ using guided ion beam experiments and theory

   https://doi.org/10.1039/C9CP06711F  

   Kim, JungSoo; M Cox, Richard; Armentrout, P. B. (February 2020, Physical Chemistry Chemical Physics)

   The kinetic energy dependent reactions of Re + with SO 2 were studied with guided ion beam tandem mass spectrometry. ReO + , ReO 2 + , and OReS + species were observed as products, all in endothermic reactions. Modeling of the kinetic energy dependent cross sections yields 0 K bond dissociation energies (BDEs, in eV) of 4.78 ± 0.06 (Re + –O), 5.75 ± 0.02 (Re + –O 2 ), and 4.35 ± 0.14 (Re + –SO). The latter two values can be combined with other information to derive the additional values 6.05 ± 0.05 (ORe + –O) and 4.89 ± 0.19 (ORe + –S). BDEs of ReO + and ReO 2 + agree with literature values whereas the values for OReS + are the first measurements. The former result is obtained even though formation of ground state ReO + is spin-forbidden. Quantum mechanical calculations at the B3LYP level of theory with a def2-TZVPPD basis set yield results that agree reasonably well with experimental values. Additional calculations at the BP86 and CCSD(T) levels of theory using def2-QZVPPD and aug-cc-pVxZ (x = T, Q, and 5) basis sets were performed to compare thermochemistry with experiment to determine that ReO 2 + rather than the isobaric ReS + is formed. Product ground states are 3 Δ 3 (ReO + ), 3 B 1 (OReO + ), 5 Π −1 (ReS + ), and 3 A′′(OReS + ) after including empirical spin–orbit corrections, which means that formation of ground state products is spin-forbidden for all three product channels. The potential energy surfaces for the ReSO 2 + system were also explored at the B3LYP/def2-TZVPPD level and exhibited no barriers in excess of the endothermicities for all products. BDEs for rhenium oxide and sulfide diatomics and triatomics are compared and discussed. The present result for formation of ReO + is compared to that for formation of ReO + in the reactions of Re + + O 2 and CO, where the former system exhibited interesting dual cross section features. Results are consistent with the hypothesis that the distinction of in-plane and out-of-plane C S symmetry in the triatomic systems might be the explanation for the two endothermic features observed in the Re + + O 2 reaction. 

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