The momentum space perspective of a typical dissociative reaction viz. that of H2O along aC2ν constrained path is brought out. The tool for the investigation of such a reaction path is provided by the distinctive topography of molecular electron momentum densities (EMD's). The EMD as well as Laplacian of EMD atp=0 are seen to follow the reaction path. The most important outcome of this work is that the information aroundp=0 seems to be sufficient for the momentum space follow-up of a chemical reaction. Qualitative features of the EMD topography for this reaction seem to remain unaffected by the choice of basis-set beyond double-zeta quality. The inclusion of correlation has seemingly no major effects on the qualitative nature of molecular EMD topographies.