SIMBAD references

High levels of deuterium fraction in N₂H⁺ are observed in some pre-stellar cores. Single-zone chemical models find that the timescale required to reach observed values (D_frac^N2H⁺\equivN₂D⁺/N₂H⁺>rsim0.1) is longer than the free-fall time, possibly 10 times longer. Here, we explore the deuteration of turbulent, magnetized cores with 3D magnetohydrodynamics simulations. We use an approximate chemical model to follow the growth in abundances of N₂H⁺ and N₂D⁺. We then examine the dynamics of the core using each tracer for comparison to observations. We find that the velocity dispersion of the core as traced by N₂D⁺ appears slightly sub-virial compared to predictions of the Turbulent Core Model of McKee & Tan, except at late times just before the onset of protostar formation. By varying the initial mass surface density, the magnetic energy, the chemical age, and the ortho-to-para ratio of H₂, we also determine the physical and temporal properties required for high deuteration. We find that low initial ortho-to-para ratios (\lesssim0.01) and/or multiple free-fall times (>rsim3) of prior chemical evolution are necessary to reach the observed values of deuterium fraction in pre-stellar cores.