DPS 35th Meeting, 1-6 September 2003
Session 40. Outer Planets/Gas Giants IV
Poster, Highlighted on, Friday, September 5, 2003, 3:30-6:00pm, Sierra Ballroom I-II

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[40.10] Ortho-Para Conversion in Collisions of H2 with H2

D. L. Huestis (SRI International)

Molecular hydrogen is the main constituent of the atmospheres of the gas giant planets, Jupiter, Saturn, Uranus, and Neptune. The relative abundances of ortho- and parahydrogen are inferred from infrared spectra of the S(1) and S(0) quadrupole transitions near 17 and 28 microns, which sample conditions in the stratosphere and upper troposphere [1,2]. At most altitudes and latitudes the ortho/para ratio is not in statistical equilibrium at the local temperature, which is interpreted as resulting from vertical transport from lower hotter regions. In order to make inferences about atmospheric circulation we need reliable information about the rate of ortho-para conversion. Atmospheric modelers estimate that it takes 30 to 100 years [1,2].

The two candidate mechanisms are collisions with paramagnetic aerosols and with weak magnetic moment of ortho-H2. The better known mechanisms involving ions or H atoms are inoperative at the relevant low altitudes and low temperatures. Here we review the available information and conclude that magnetic interactions between hydrogen molecules will lead to interconversion in only about 5 years. We also outline theoretical procedures for quantum coupled channels calculations.

[1] B. J. Conrath and P. J. Gierasch, Icarus 57, 184 (1984).

[2] T. Fouchet, E. Lellouch, and H. Feuchtgruber, Icarus 161, 127 (2003).

The author(s) of this abstract have provided an email address for comments about the abstract: david.huestis@sri.com

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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.