Hydrogen
The converter we built to produce 99.99% enriched para-H2
"Team Hydrogen" is studying the physics of H3+, an important interstellar species, by observing its para and ortho quantum states.
The liquid helium dewar in which solid hydrogen crystals are grown.
Nuclear Spin Modifications of Hydrogen
The terms 'para' and 'ortho' refer to the combined orientation of nuclear spin in the protons that make up the molecule. Nucleons (i.e. protons and neutrons), like electrons, possess an intrinsic angular momentum otherwise known as spin. Because nucleons are also fermions, this spin exists in half-integer quanta. Taking the hydrogen molecule H2 as an example, in the para configuration, the spins of the two protons combine antisymmetrically, thereby resulting in an overall spin of zero. In the ortho configuration, the spins combine symmetrically and sum to one. Extrapolating this idea to the H3+ molecule, we observe the para configuration (I=1/2), with two protons spin aligned and one anti-aligned, as well as the ortho configuration (I=3/2) in which all three nucleon spins are aligned.
Ions dissociatively recombine with electrons in this section of the CRYRING ion storage ring.
Dissociative Recombination
We used the CRYRING ion storage ring in Stockholm, Sweden to measure electron recombination with para H3+. CRYRING has characteristics that make it possible to observe recombination behaviors for specific energy states of molecules. Theoretical predictions assert that the recombination rate has a dependence on the nuclear spin configuration of H3+, and our preliminary measurements [along with those of Kreckel et al., Phys. Rev. Lett. (2005) 95, 263205] have verified this.
A supersonic expansion of hydrogen diluted in neon.
H3+ + H2 Reaction
In addition to studying the dissociative recombination cross section of different H3+ spin modifications, we have used the different spin species to observe the reaction of H3+ with H2. This is accomplished using continuous wave cavity ringdown spectroscopy to probe a supersonically expanding hydrogenic plasma, which enables us to observe the branching ratios for various proton exchange pathways between H3+ and H2 at astrophysically relevant temperatures. We are also using direct absorption spectroscopy to study this reaction at warmer temperatures (but still cold; between 120-180 K) in the liquid nitrogen-cooled plasma of a hollow cathode.
The dissociative recombination spectrum of a hydrogenic plasma that is ~49.1% para-H3+ and one that is enriched to ~83.6% para-H3+. Ed represents the electron energy in the ion frame (Eion - Eelectron).
What we learn from this ongoing recombination and reaction research, combined with astrophysical observations, will increase our understanding of the chemistry and physics of hydrogen in the interstellar medium, and could impact the way H3+ is used as a probe of astrophysical conditions in these regions of space.
Production and Properties of para-H2
Additionally, we recently concluded a study to optimize methods for para-H2 production and enrichment analysis, and are currently measuring optical properties of solid hydrogen crystals.
Related Content
Papers
| 39 | B. A. Tom, S. Bhasker, Y. Miyamoto, T. Momose, and B. J. McCall "Producing and Quantifying Enriched Para-H2" Review of Scientific Instruments (2009), 80, 016108. |
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| 38 | B. A. Tom, V. Zhaunerchyk, M. B. Wiczer, A. A. Mills, K. N. Crabtree, M. Kaminska, W. D. Geppert, M. Hamberg, M. af Ugglas, E. Vigren, W. J. van der Zande, M. Larsson, R. D. Thomas, and B. J. McCall "Dissociative Recombination of Highly Enriched Para-H3+" Journal of Chemical Physics (2009), 130, 031101. |
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| 36 | M. Larsson, B. J. McCall and A. E. Orel "The Dissociative Recombination of H3+ -- A Saga Coming to an End?" Chemical Physics Letters (2008), 462, 145-151. |
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| 31 | B. J. McCall "Dissociative Recombination of Cold H3+ and its Interstellar Implications" Philosophical Transactions of the Royal Society of London Series A (2006), 364, 2953-2963. |
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Talks
| 68 | B. A. McGuire, B. A. Tom, L. E. Moore, T. J. Wood and B. J. McCall "Spectroscopic Studies of the H3+ + H2 Reaction at Astrophysically Relevant Temperatures" Sixty-Fourth International Symposium on Molecular Spectroscopy, The Ohio State University, Columbus, OH, 2009. |
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| 60 | B. J. McCall "H3+: The Simplest Polyatomic Molecule in the Laboratory and in the Interstellar Medium" Advancing Chemical Understanding Through Astronomical Observations, Green Bank Telescope, Green Bank, WV, 2009. |
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| 59 | B. J. McCall "Spectroscopic Study of the Astrophysically Important Reaction Between H3+ and H2" Gordon Conference on Gaseous Ions, Galveston, TX, 2009. |
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| 57 | B. A. Tom, M. B. Wiczer, A. A. Mills, K. N. Crabtree and B. J. McCall "The H3+ + H2 Reaction: A Possible Mechanism for para-H3+ Enrichment in the Diffuse Interstellar Medium" Inaugural Midwest Astrochemistry Meeting, University of Illinois, 2008. |
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| 56 | B. J. McCall "New Laboratory and Theoretical Studies of Astrophysically Important Reactions of H3+" Gordon Conference on Atomic and Molecular Interactions, New London, New Hampshire, 2008. |
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| 46 | B. A. Tom, M. B. Wiczer, A. A. Mills, K. N. Crabtree, and B. J. McCall "Observation of Nuclear Spin Selection Rules in Supersonically Expanding Plasmas Containing H3+" Sixty-Third International Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, 2008. |
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| 45 | B. J. McCall "H3+: A Case Study for the Importance of Molecular Laboratory Astrophysics" American Astronomical Society National Meeting, St. Louis, Missouri, 2008. |
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| 38 | B. A. Tom, B. J. McCall, Y. Miyamoto, and T. Momose "The Index of Refraction of Solid Hydrogen" Sixty-Second International Symposium on Molecular Spectroscopy, Ohio State University, Columbus, OH, 2007. |
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Posters
| 12 | B. A. Tom, B. A. McGuire, L. E. Moore, T. J. Wood and B. J. McCall "Hydrogenic Plasmas in a Cold Hollow Cathode" Advancing Chemical Understanding Through Astronomical Observations, Green Bank Telescope, Green Bank, WV, 2009. |
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Other Publications
| 19 | B. A. Tom "Nuclear Spin Dependence in Reactions of H3+ in the Laboratory and the Interstellar Medium" Ph.D. Thesis, University of Illinois, 2009. |
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| 18 | B. A. McGuire "Design and Implementation of a Liquid Nitrogen-Cooled Hollow Cathode Discharge Source for the Study of the Reaction H3+ + H2 → H2 + H3+ at Physically Relevant Temperatures and the Study of the B3Πg → A3Σu+ Band System of N2" B. S. Thesis, University of Illinois, 2009. |
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| 17 | B. A. Tom "Reactions Involving the Nuclear Spin Modifications of H3+ and H2; Implications for the Interstellar Medium" Research Prospectus for Preliminary Examination, University of Illinois, 2008. |
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