Deuterium chemistry and airglow in the jovian thermosphere

Abstract

We present a detailed study of the distribution of key deuterated species (viz., atomic D and HD) and the associated deuterium Lyman- α airglow in the jovian thermosphere. The reactions that appear to govern the abundances of these deuterated species are used in conjunction with C 2-chemistry in a 1-D photochemical-diffusion model. While the D abundance is mainly sensitive to H densities and the vibrational temperature profile, the D vertical distribution also depends on other parameters such as eddy mixing and the uncertain values of some of the reaction rate constants. We consider different scenarios by varying several parameters controlling the D distribution in the thermosphere. A radiative transfer model with coupling of the H and D Lyman- α lines is employed to obtain line profiles and total intensities at disk center for these scenarios. This allows a comparison of the impact of various parameters on the jovian D Lyman- α emission. A consequence of these chemical processes in the jovian thermosphere is the formation of CH 2D, CH 3D, and C 2H 5D, and other deuterated species. We also discuss the source of these deuterated hydrocarbons and their abundance. We find that HD vibrational chemistry impacts D in the thermosphere, CH 3D and C 2H 5D are vibrationally enhanced in the thermosphere, and variations in abundance of CH 3D and C 2H 5D in the thermosphere may reflect dynamical activity (i.e., K h ) in the jovian upper atmosphere. An observing program dedicated to providing such measurements of these testable phenomena would provide further insight into the synergistic coupling between chemistry, energetics and airglow in the jovian upper atmosphere.