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Hydrogen Dimers in Giant-planet Infrared Spectra
Department of Physics and Astronomy, University of Leicester.
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.ORCID iD: 0000-0002-7629-0169
Jet Propulsion Laboratory, California Institute of Technology.
2018 (English)In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 235, no 1, article id 24Article in journal (Refereed) Published
Abstract [en]

Despite being one of the weakest dimers in nature, low-spectral-resolution Voyager/IRIS observations revealed the presence of (H2)2 dimers on Jupiter and Saturn in the 1980s. However, the collision-induced H2-H2 opacity databases widely used in planetary science have thus far only included free-to-free transitions and have neglected the contributions of dimers. Dimer spectra have both fine-scale structure near the S(0) and S(1) quadrupole lines (354 and 587 cm-1, respectively), and broad continuum absorption contributions up to ±50 cm-1 from the line centers. We develop a new ab initio model for the free-to-bound, bound-to-free, and bound-to-bound transitions of the hydrogen dimer for a range of temperatures (40-400 K) and para-hydrogen fractions (0.25-1.0). The model is validated against low-temperature laboratory experiments, and used to simulate the spectra of the giant planets. The new collision-induced opacity database permits high-resolution (0.5-1.0 cm-1) spectral modeling of dimer spectra near S(0) and S(1) in both Cassini Composite Infrared Spectrometer observations of Jupiter and Saturn, and in Spitzer Infrared Spectrometer (IRS) observations of Uranus and Neptune for the first time. Furthermore, the model reproduces the dimer signatures observed in Voyager/IRIS data near S(0) on Jupiter and Saturn, and generally lowers the amount of para-H2 (and the extent of disequilibrium) required to reproduce IRIS observations.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2018. Vol. 235, no 1, article id 24
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Other Physics Topics
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Applied Physics
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URN: urn:nbn:se:ltu:diva-68168DOI: 10.3847/1538-4365/aaa07aISI: 000427637800004Scopus ID: 2-s2.0-85044126669OAI: oai:DiVA.org:ltu-68168DiVA, id: diva2:1195182
Note

Validerad;2018;Nivå 2;2018-04-04 (andbra)

Available from: 2018-04-04 Created: 2018-04-04 Last updated: 2018-04-06Bibliographically approved

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