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1. Conversion of He(2 ³ S ) to He ₂ ( a ³ Σ _u ⁺ ) in Liquid Helium

   https://doi.org/10.1021/acs.jpclett.8b02454  

   Nijjar, P. ; Krylov, A. I. ; Prezhdo, O. V. ; Vilesov, A. F. ; Wittig, C. ( September 2018 , The Journal of Physical Chemistry Letters)
2. Hot and Heterogenous High‐ ³ He/ ⁴ He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island

   https://doi.org/10.1029/2019GC008654  

   Willhite, Lori N. ; Jackson, Matthew G. ; Blichert‐Toft, Janne ; Bindeman, Ilya ; Kurz, Mark D. ; Halldórsson, Sæmundur A. ; Harðardóttir, Sunna ; Gazel, Esteban ; Price, Allison A. ; Byerly, Benjamin L. ( December 2019 , Geochemistry, Geophysics, Geosystems)
3. Recycled Components in Mantle Plumes Deduced From Variations in Halogens (Cl, Br, and I), Trace Elements, and ³ He/ ⁴ He Along the Hawaiian-Emperor Seamount Chain

   https://doi.org/10.1029/2018GC007959  

   Broadley, Michael W. ; Sumino, Hirochika ; Graham, David W. ; Burgess, Ray ; Ballentine, Chris J. ( January 2019 , Geochemistry, Geophysics, Geosystems)
4. High ³ He/ ⁴ He in central Panama reveals a distal connection to the Galápagos plume

   https://doi.org/10.1073/pnas.2110997118  

   Bekaert, David V. ; Gazel, Esteban ; Turner, Stephen ; Behn, Mark D. ; de Moor, J. Marten ; Zahirovic, Sabin ; Manea, Vlad C. ; Hoernle, Kaj ; Fischer, Tobias P. ; Hammerstrom, Alexander ; et al ( November 2021 , Proceedings of the National Academy of Sciences)

   It is well established that mantle plumes are the main conduits for upwelling geochemically enriched material from Earth's deep interior. The fashion and extent to which lateral flow processes at shallow depths may disperse enriched mantle material far (>1,000 km) from vertical plume conduits, however, remain poorly constrained. Here, we report He and C isotope data from 65 hydrothermal fluids from the southern Central America Margin (CAM) which reveal strikingly high 3 He/ 4 He (up to 8.9R A ) in low-temperature (≤50 °C) geothermal springs of central Panama that are not associated with active volcanism. Following radiogenic correction, these data imply a mantle source 3 He/ 4 He >10.3R A (and potentially up to 26R A , similar to Galápagos hotspot lavas) markedly greater than the upper mantle range (8 ± 1R A ). Lava geochemistry (Pb isotopes, Nb/U, and Ce/Pb) and geophysical constraints show that high 3 He/ 4 He values in central Panama are likely derived from the infiltration of a Galápagos plume–like mantle through a slab window that opened ∼8 Mya. Two potential transport mechanisms can explain the connection between the Galápagos plume and the slab window: 1) sublithospheric transport of Galápagos plume material channeled by lithospheremore »thinning along the Panama Fracture Zone or 2) active upwelling of Galápagos plume material blown by a “mantle wind” toward the CAM. We present a model of global mantle flow that supports the second mechanism, whereby most of the eastward transport of Galápagos plume material occurs in the shallow asthenosphere. These findings underscore the potential for lateral mantle flow to transport mantle geochemical heterogeneities thousands of kilometers away from plume conduits.« less
5. Plasma-droplet interaction study to assess transport limitations and the role of ^⋅ OH, O ^⋅ ,H ^⋅ ,O ₂ (a ¹ Δ _g ),O ₃ , He(2 ³ S) and Ar(1s ₅ ) in formate decomposition

   https://doi.org/10.1088/1361-6595/ac2676  

   Nayak, Gaurav ; Oinuma, Gaku ; Yue, Yuanfu ; Santos Sousa, João ; Bruggeman, Peter J ( November 2021 , Plasma Sources Science and Technology)

   Abstract Plasmas interacting with liquid microdroplets are gaining momentum due to their ability to significantly enhance the reactivity transfer from the gas phase plasma to the liquid. This is, for example, critically important for efficiently decomposing organic pollutants in water. In this contribution, the role of ⋅ OH as well as non- ⋅ OH-driven chemistry initiated by the activation of small water microdroplets in a controlled environment by diffuse RF glow discharge in He with different gas admixtures (Ar, O 2 and humidified He) at atmospheric pressure is quantified. The effect of short-lived radicals such as O ⋅ and H ⋅ atoms, singlet delta oxygen (O 2 ( a 1 Δ g )), O 3 and metastable atoms of He and Ar, besides ⋅ OH radicals, on the decomposition of formate dissolved in droplets was analyzed using detailed plasma diagnostics, droplet characterization and ex situ chemical analysis of the treated droplets. The formate decomposition increased with increasing droplet residence time in the plasma, with ∼70% decomposition occurring within ∼15 ms of the plasma treatment time. The formate oxidation in the droplets is shown to be limited by the gas phase ⋅ OH flux at lower H 2 O concentrations with amore »significant enhancement in the formate decomposition at the lowest water concentration, attributed to e − /ion-induced reactions. However, the oxidation is diffusion limited in the liquid phase at higher gaseous ⋅ OH concentrations. The formate decomposition in He/O 2 plasma was similar, although with an order of magnitude higher O ⋅ radical density than the ⋅ OH density in the corresponding He/H 2 O plasma. Using a one-dimensional reaction–diffusion model, we showed that O 2 ( a 1 Δ g ) and O 3 did not play a significant role and the decomposition was due to O ⋅ , and possibly ⋅ OH generated in the vapor containing droplet-plasma boundary layer.« less