Presentation #102.02 in the session “Chemistry in Cometary Comae”.
The ammonia molecule has traditionally been considered to be the solo parent of the NH2 radical in cometary comae because photo-dissociation reactions of ammonia molecules by solar UV radiation can produce NH2 radicals efficiently. Also ammonia has generally been assumed to be the most abundant N-bearing molecule in comets. Although ammonia molecules have been believed to be stored in the cometary ices, the recent in-situ observations by the Rosetta spacecraft revealed that some kinds of ammonium salts might contribute to the production of ammonia molecules in the very inner coma. This scenario could change the traditional picture about the origin of ammonia molecules in comets. Cascading dissociation reactions from ammonium salt(s) to ammonia, and then to NH2, can only be investigated based on high-S/N spatial profiles of NH2 and ammonia in cometary comae. High-resolution ground-based infrared spectra of comet C/2014 Q2 (Lovejoy) were obtained with NIRSPEC mounted on the Keck2 telescope on two post-perihelion dates (UT 2015 February 2 and 3), when the comet was at a heliocentric distance of 1.29 au. We extracted high-S/N spatial profiles not only of NH2 but also of ammonia in the comet. In order to reproduce the spatial profiles of NH2 and ammonia, we have developed Monte-Carlo simulation codes. We will discuss the possibility of ammonium salts as a parent of ammonia in cometary comae.