Enhancement of Deuterated Ethane on Jupiter

Abstract

We report laboratory measurements of cross sections of CH 3 D and C 2 H 5 D in the extreme ultraviolet. The results are incorporated in a photochemical model for the deuterated hydrocarbons up to C2 in the upper atmosphere of Jupiter, taking into account the fast reactions for exchanging H and D atoms between H 2 and CH 4 , H ϩ ,. Since there is no reliable kinetics measurement for the reaction, HD ↔ D ϩ H CH ϩ D ↔ CH D ϩ H 2 3 2 , we use Yung et al.'s estimate for its rate constant. The strong temperature dependence CH D ϩ H r CH ϩ D 2 3 for this reaction leads to large isotopic fractionation for CH 3 D and C 2 H 5 D in the upper atmosphere of Jupiter, where their production rates depend on the abundance of deuterated methyl radical. The model predicts that the D/H ratio in deuterated ethane is about 15 times that of the bulk atmosphere. A confirmation of this result would provide a sensitive test of the photochemistry of hydrocarbons in the atmosphere of Jupiter.

Vacuum-UV spectroscopy of interstellar ice analogs

“…This feature is attributed to the 1t 2 -3s (D 2d ) Rydberg transition. We detected a small bump near 140 nm (8.85 eV), which was not observed by Wu et al (2012) in the solid phase or by Lee et al (2001) in the gas phase. This feature may be produced by the VUV-absorption of a photoproduct.…”

“…VUV-absorption cross section as a function of photon wavelength (bottom X-axis) and VUV-photon energy (top X-axis) of CH 4 ice deposited at 8 K, black solid trace. The blue dashed trace is the VUV-absorption cross-section spectrum of gas phase CH 4 adapted from Lee et al (2001). The fit of the solid-phase spectrum, red dotted (single bands, see Table 2) and dashed-dotted trace, is the sum of three Gaussians.…”

“…Gas-phase data from Lee et al (2001) were used for comparison with our solid-phase data, see Fig. 1, following Wu et al (2012).…”

ABSORPTION CROSS SECTION OF GASEOUS ACETYLENE AT 85 K IN THE WAVELENGTH RANGE 110-155 nm

“…To assess the abundances and photochemically induced changes in space, one must have quantitative information about the absorption cross sections of interstellar molecules in the VUV range (Miller & Yung 2000). For this purpose, we determined the absorption cross sections of several interstellar molecular species in the VUV range (Cheng et al 1999(Cheng et al , 2002(Cheng et al , 2004(Cheng et al , 2006Bahou et al 2001;Lee et al 2001;Liang et al 2007), but most such measurements were made near 300 K.…”

Absorption cross section of molecular oxygen in the transition E3Σu-v= 0 – X3Σg-v= 0 at 38 K

“…We determined the absorption cross sections of several interstellar molecular species in this range (H 2 O, Cheng et al 1999Cheng et al , 2004HCl, Bahou et al 2001;CH 4 , Lee et al 2001;CH 3 OH, Cheng et al 2002;NH 3 , Cheng et al 2006;and Liang et al 2007), but most measurements were made near 300 K. One problem in the application of these data to the photochemical model is that in outer space the temperature is much less than 300 K: for example, the relevant atmospheric temperature is ∼170 K for Jupiter, ∼140 K for Saturn, ∼120 K for Titan, ∼50 K for Triton, and even lower for Neptune and Uranus (Yung & DeMore 1999). Molecular absorption cross sections measured near 300 K are generally inadequate to explain the observed spectral features and to allow an accurate determination of the abundance of atmospheric constituents in outer space.…”