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1. Laser-cooling Cadmium Bosons and Fermions with Near Ultraviolet Triplet Excitations

   https://doi.org/10.1088/1742-6596/2889/1/012006  

   Gibble, Kurt (November 2024, Journal of Physics: Conference Series)

   Abstract Cadmium is laser-cooled and trapped with excitations to triplet states with UVA light, first using only the 67 kHz wide 326 nm intercombination line and subsequently, for large loading rates, the 25 MHz wide 361 nm³P₂→³D₃transition. Eschewing the hard UV 229 nm¹S₀→¹P₁transition, only small magnetic fields gradients, less than 6 G cm⁻¹, are required enabling a 100% transfer of atoms from the 361 nm trap to the 326 nm narrow-line trap. All 8 stable cadmium isotopes are straightforwardly trapped, including two nuclear-spin- $\frac{1}{2}$fermions that require no additional repumping. We observe evidence of³P₂collisions limiting the number of trapped metastable atoms, report isotope shifts for¹¹¹Cd and¹¹³Cd of the 326 nm¹S₀→³P₁, 480nm³P₁→³S₁, and 361 nm³P₂→³D₃transitions, and measure the¹¹⁴Cd 5s5p³P₂→ 5s5d³D₃transition frequency to be 830 096 573(15) MHz. 

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2. Panning for Gold: New Emission Lines from UV–VIS Spectroscopy of AuI and AuII

   Bromley, S. J.; et al. (September 2020, The Astrophysical journal Supplement series)

   The recent detection of a neutron star merger by the LIGO collaboration has renewed interest in laboratory studies of r-process elements. Accurate modeling and interpretation of the electromagnetic transients following the mergers requires computationally expensive calculations of both the structure and opacity of all trans-iron elements. To date, the necessary atomic data to benchmark structure codes are incomplete or, in some cases, absent entirely. Within the available laboratory studies, the literature on Au I and Au II provides incomplete reports of the emission lines and level structures. We present a new study of Au I and Au II lines and levels by exposing a solid gold target to plasma in the Compact Toroidal Hybrid (CTH) experiment at Auburn University. A wavelength range from 187 to 800nm was studied. In Au I, 86 lines are observed, 43 of which are unreported in the literature, and the energies of 18 5d96s6plevels and 16 of the 18 known 5d96s6dlevels are corroborated by a least-squares level energy optimization. In Au II, 76 emission lines are observed, and 51 of the lines are unreported in the literature. For both Au I and Au II, the new lines predominantly originate from the most energetic of the known levels, and over half of the new Au II lines have wavelengths longer than 300 nm. For the estimated electron parameters of CTH plasmas at the gold target (ne∼1012 cm−3, Te∼10 eV), two-electron transitions are similar in intensity to LS-allowed one-electron transitions. 

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3. Panning for Gold: New Emission Lines from UV–VIS Spectroscopy of Au I and Au II

   https://doi.org/10.3847/1538-4365/abaa4d  

   Bromley, S. J.; Johnson, C. A.; Ennis, D. A.; Hartwell, G. J.; Maurer, D. A.; Loch, S.D.; Stancil, P.C.; McLaughlin, B. M.; Sosolik, C. E.; Marler, J. P. (October 2020, The astrophysical journal)

   The recent detection of a neutron star merger by the LIGO collaboration has renewed interest in laboratory studies of r-process elements. Accurate modeling and interpretation of the electromagnetic transients following the mergers requires computationally expensive calculations of both the structure and opacity of all trans-iron elements. To date, the necessary atomic data to benchmark structure codes are incomplete or, in some cases, absent entirely. Within the available laboratory studies, the literature on Au I and Au II provides incomplete reports of the emission lines and level structures. We present a new study of Au I and Au II lines and levels by exposing a solid gold target to plasma in the Compact Toroidal Hybrid (CTH) experiment at Auburn University. A wavelength range from 187 to 800 nm was studied. In Au I, 86 lines are observed, 43 of which are unreported in the literature, and the energies of 18 5d9 6s 6p levels and 16 of the 18 known 5d9 6s 6d levels are corroborated by a least-squares level energy optimization. In Au II, 76 emission lines are observed, and 51 of the lines are unreported in the literature. For both Au I and Au II, the new lines predominantly originate from the most energetic of the known levels, and over half of the new Au II lines have wavelengths longer than 300 nm. For the estimated electron parameters of CTH plasmas at the gold target (ne~10^12 cm−3, Te~10 eV), two-electron transitions are similar in intensity to LS-allowed one-electron transitions. 

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4. Atomic Transition Probabilities for Transitions of Si i and Si ii and the Silicon Abundances of Several Very Metal-poor Stars ^∗

   https://doi.org/10.3847/1538-4365/acb642  

   Den Hartog, E. A.; Lawler, J. E.; Sneden, C.; Roederer, I. U.; Cowan, J. J. (March 2023, The Astrophysical Journal Supplement Series)

   Abstract We report new measurements of branching fractions for 20 UV and blue lines in the spectrum of neutral silicon (Si i ) originating in the 3 s 2 3 p 4 s 3 P o 1,2 , 1 P o 1 , and 3 s 3 p 3 1 D o 1,2 upper levels. Transitions studied include both strong, nearly pure LS multiplets as well as very weak spin-forbidden transitions connected to these upper levels. We also report a new branching fraction measurement of the 4 P 1/2 – 2 P o 1/2,3/2 intercombination lines in the spectrum of singly ionized silicon (Si ii ). The weak spin-forbidden lines of Si i and Si ii provide a stringent test on recent theoretical calculations, to which we make comparison. The branching fractions from this study are combined with previously reported radiative lifetimes to yield transition probabilities and log( gf ) values for these lines. We apply these new measurements to abundance determinations in five metal-poor stars. 

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5. A new interpretation of the structure and solvent dependence of the far UV circular dichroism spectrum of short oligopeptides

   https://doi.org/10.1039/c9cc01513b  

   Kumar, Anshuman; Schweitzer-Stenner, Reinhard; Wong, Bryan M. (May 2019, Chemical Communications)

   UV circular dichroism (UVCD) spectroscopy is a prominent tool for exploring secondary structures of polypeptides and proteins. In the unfolded state of these biomolecules, most of the individual residues primarily sample a conformation called polyproline II. Its CD spectrum contains a negatively biased positive couplet with a pronounced negative maximum below and a weak positive maximum above 200 nm. It is traditionally rationalized in terms of an excitonic coupling mechanism augmented by polarization effects. In this work, we carry out new time-dependent density functional theory calculations on the cationic tripeptide GAG in implicit and explicit water to determine the transitions that give rise to the observed CD signals of polyproline II and β-strand conformations. Our results reveal a plethora of electronic transitions that are governed by configurational interactions between multiple molecular orbital transitions of comparable energy. We also show that reproducing the CD spectra of polyproline II and β-strand conformations requires the explicit consideration of water molecules. The structure dependence of delocalized occupied orbitals contributes to the experimentally-observed invalidation of Flory's isolated pair hypothesis. 

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