An Approach to Estimate the Binding energy of Interstellar Species

One of the major obstacles to accurately model the interstellar chemistry is an inadequate knowledge about the binding energy (BE) of interstellar species with dust grains. In denser region of molecular cloud, where very complex chemistry is active, interstellar dust is predominantly covered by H2O molecules and thus it is essential to know the interaction of gas phase species with water ice to trace realistic physical and chemical processes. To this effect, we consider water (cluster) ice to calculate the BE of several atoms, molecules, and radicals of astrochemical interest. Systematic studies have been carried out to come up with a relatively more accurate BE of astrophysically relevant species on water ice. We increase the size of the water cluster methodically to capture the realistic situation. Sequentially one, three, four, five and six water molecules are considered to represent water ice analogue in increasing order of complexity. We notice that for most of the species considered here, as we increase the cluster size, our calculated BE value starts to converge towards the experimentally obtained value. More specifically, our computed results with water c-pentamer (average deviation from experiment ~ 15.8%) and c-hexamer (chair) (average deviation from experiment ~ 16.7%) configuration are found to be more nearer as the experimentally obtained value than other water clusters considered.