The role of ion-molecule elastic collisions (specifically D+−D2 collisions) in strongly detached divertor conditions has been studied in the MAST-U Super-X configuration using SOLPS-ITER. Two strongly detached steady state solutions, one obtained through a main-ion (D2) fuelling scan and the other through an impurity (N) seeding scan at fixed fuelling rate, were compared and a significant difference in the volume recombination levels was observed. Higher divertor plasma densities and temperatures lower than 1eV are achieved in the non-seeded case, resulting in volume recombination playing the key role in reducing the plasma flux reaching the target. On the other hand,volume recombination levels are negligible in the seeded case due to the temperatures not falling significantly below 1eV and generally lower divertor plasma densities. Further, the divertor density profiles were qualitatively different between the two cases: in the non-seeded case, a significant increase in density is observed across the divertor with the profile strongly peaked near the target whereas in the non-seeded case, there is little change in density across the divertor and the profile is mostly flat. We are able to recover features of seeded case, i.e. flat density profile,higher temperatures and negligible recombination, by turning off ion-molecule elastic collisions in the non-seeded case. Analysis shows that as the temperature drops and approaches 1eV, important power loss mechanisms like impurity radiation and deuterium excitation/ionisation weaken significantly; and ion-molecule elastic collisions are necessary for further heat dissipation and access to the sub-eV temperatures needed for recombination to become important. When ion-molecule elastic collisions are turned off, no other significant power loss mechanism is present as the temperature approaches 1eV and as a result, sub-eV temperatures are not accessed. Further, we find that ion-molecule elastic collisions introduce a significant drag on the plasma flowing towards the target in the non-seeded case – they effectively ‘plug’ the plasma flow which is what leads to a significant increase in the density across the divertor. Turning off ion-molecule elastic collisions allows the plasma to flow freely to the target leading to a flat density profile. In the seeded case, energy and momentum dissipated through ion-molecule elastic collisions is a lot weaker compared to the non-seeded case – in general, this is expected due to the lower plasma and molecule densities in the divertor. In addition, our analysis suggests that the impact of ion-molecule elastic in the seeded case is weakened further as a result of high impurity levels in the divertor – we find that the presence of a large amount of singly ionised nitrogen which does not interact with any neutrals, essentially acts like a reservoir of energy and momentum. In general, our analysis suggests that elastic collisions between neutrals and ions (deuterium or impurities) are likely to introduce a significant amount of drag on the divertor plasma flowing to the target, and therefore have a strong impact on the divertor density profile in strongly detached Super-X plasmas. They are also likely to play an important role inheat dissipation at temperatures ≤1eV. Finally, our analysis shows that the qualitative differences observed between the seeded and non-seeded cases is likely due to the fact that energy and momentum exchange between neutrals and impurity ions is included in our model – key impurity-neutral interactions need to be identified in order to accurately model strongly detached Super-X plasmas achieved through impurity seeding.