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We investigate the water deuteration ratio and ortho-to-para nuclear spinratio of H2 (OPR(H2)) during the formation and early evolution of a molecularcloud, following the scenario that accretion flows sweep and accumulate HI gasto form molecular clouds. We follow the physical evolution of post-shockmaterials using a one-dimensional shock model, with post-processing gas-icechemistry simulations. This approach allows us to study the evolution of theOPR(H2) and water deuteration ratio without an arbitrary assumption concerningthe initial molecular abundances, including the initial OPR(H2). When theconversion of hydrogen into H2 is almost complete, the OPR(H2) is already muchsmaller than the statistical value of three due to the spin conversion in thegas phase. As the gas accumulates, the OPR(H2) decreases in a non-equilibriummanner. We find that water ice can be deuterium-poor at the end of its mainformation stage in the cloud, compared to water vapor observed in the vicinityof low-mass protostars where water ice is likely sublimated. If this is thecase, the enrichment of deuterium in water should mostly occur at somewhatlater evolutionary stages of star formation, i.e., cold prestellar/protostellarcores. The main mechanism to suppress water ice deuteration in the cloud is thecycle of photodissociation and reformation of water ice, which efficientlyremoves deuterium from water ice chemistry. The removal efficiency depends onthe main formation pathway of water ice. The OPR(H2) plays a minor role inwater ice deuteration at the main formation stage of water ice.

Water deuteration and ortho-to-para nuclear spin ratio of H2 in molecular clouds formed via the accumulation of HI gas