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N-bearing molecules (like N2H+ or NH3) are excellent tracers of high-density,low-temperature regions like dense cloud cores and could shed light intosnowlines in protoplanetary disks and the chemical evolution of comets.However, uncertainties exist about the grain surface chemistry of thesemolecules -- which could play an important role in their formation andevolution. This study explores experimentally the behaviour of NH$_3$ onsurfaces mimicking grains under interstellar conditions alongside other majorinterstellar ice components (ie. H$_2$O, CO, CO$_2$). We performedco-deposition experiments using the Ultra High Vacuum (UHV) setup VENUS (VErsdes NoUvelles Syntheses) of NH$_3$ along with other adsorbates (here, H$_2$O,$^{13}$CO and CO$_2$) and performed Temperature Programmed Desorption (TPD) andTemperature Programmed-During Exposure Desorption (TP-DED) experiments. Weobtained binding Energy (BE) distribution of NH$_3$ on Crystalline Ice(CI) andcompact-Amorphous Solid Water (c-ASW) by analyses of the TPD profiles of NH3 onthe substrates. We observe a significant delay in the desorption and a decreasein the desorption rate of NH$_3$ when H$_2$O is introduced into theco-deposited mixture of NH$_3$-$^{13}$Co or NH$_3$-CO$_2$, absent withoutH$_2$O. Secondly, H$_2$O traps nearly 5-9 per cent of the co-deposited NH3,released during water's amorphous-to-crystalline phase change. Thirdly, for CI,we obtained a BE distribution between 3780K-4080K, and c-ASW between3780K-5280K -- using a pre-exponential factor A = 1.94$\times 10^{15}$/s. Weconclude that NH$_3$ behaviour is significantly influenced by the presence ofH$_2$O due to the formation of hydrogen bonds, in line with quantumcalculations. This interaction preserves NH$_3$ on grain surfaces to highertemperatures making it available to the central protostar in protoplanetarydisks. It also explains why NH$_3$ freeze out in pre-stellar cores isefficient.

Experimental study of the binding energy of NH3 on different types of ice and its impact on the snow line of NH3 and H2O