37th DPS Meeting, 4-9 September 2005
Session 60 Planetary Magnetospheres
Poster, Thursday, September 8, 2005, 6:00-7:15pm, Music Foyer

## [60.08] H+ + H2 Ion-Molecule Reactions in the Ionospheres of the Outer Planets

D. L. Huestis (SRI)

For the past 30 years, models of outer planet ionospheres have used estimated rate coefficients for charge transfer Reaction (1), which is a critical step in controlling the electron density. No confirmation has been available from the laboratory or theory.

(1) H+ + H2(v{\geq}4) arrow H + H2+

By analysis and extrapolation of the results from recent theoretical work [1,2] from the plasma fusion community, we suggest that Reaction (1) has a rate coefficient of approximately 1.3 \times 10-9 cm3/s, consistent with numbers in current models.

In addition, we suggest that vibrational relaxation Reaction (2) will also be fast, with rate coefficients of approximately 1.5 \times 10-9 cm3/s for v = 4-8 and 2.8 \times 10-9 cm3/s for v = 1-3.

(2) H+ + H2(vi) arrow H+ + H2(vf < vi)

Inclusion of Reaction (2) will significantly reduce calculated vibrational temperatures in ionospheric models. Protons are less abundant than neutral hydrogen atoms by a factor of about 10,000 and the proton rate coefficients for vibrational relaxation are about a factor of 10,000 larger.

[1] A. Ichihara, O. Iwamoto, and R. K. Janev, Cross Sections for the Reaction H+ + H2(v=0-14) arrow H + H2+ at Low Collision Energies," J. Phys. B. 33, 4747-4758 (2000).

[2] P.S. Krstic, Inelastic Processes from Vibrationally Excited States in Slow H+ + H2 and H + H2+ Collisions: Excitations and Charge Transfer," Phys. Rev. A 66, 042717 (2002).