Kong, ShuoShuoKongTan, Jonathan C.Jonathan C.TanCaselli, PaolaPaolaCaselliFONTANI, FRANCESCOFRANCESCOFONTANIPillai, ThusharaThusharaPillaiButler, Michael J.Michael J.ButlerShimajiri, YoshitoYoshitoShimajiriNakamura, FumitakaFumitakaNakamuraSakai, TakeshiTakeshiSakai2020-05-252020-05-2520160004-637Xhttp://hdl.handle.net/20.500.12386/25125We study deuterium fractionation in two massive starless/early-stage cores, C1-N and C1-S, in Infrared Dark Cloud G028.37+00.07, which was first identified by Tan et al. with ALMA. Line emission from multiple transitions of N<SUB>2</SUB>H<SUP>+</SUP> and N<SUB>2</SUB>D<SUP>+</SUP> were observed with the ALMA, CARMA, SMA, JCMT, NRO 45 m, and IRAM 30 m telescopes. By simultaneously fitting the spectra, we estimate the excitation conditions and deuterium fraction, {D}<SUB>{frac</SUB>}<SUP>{{{N</SUP>}}<SUB>2</SUB>{{{H}}}<SUP>+</SUP>} \equiv \quad [{{{N}}}<SUB>2</SUB>{{{D}}}<SUP>+</SUP>]/[{{{N}}}<SUB>2</SUB>{{{H}}}<SUP>+</SUP>], with values of {D}<SUB>{frac</SUB>}<SUP>{{{N</SUP>}}<SUB>2</SUB>{{{H}}}<SUP>+</SUP>} ≃ 0.2-0.7, several orders of magnitude above the cosmic [D]/[H] ratio. Additional observations of o-H<SUB>2</SUB>D<SUP>+</SUP> are also presented that help constrain the ortho-to-para ratio of H<SUB>2</SUB>, which is a key quantity affecting the degree of deuteration. We then present chemodynamical modeling of the two cores, especially exploring the implications for the collapse rate relative to free-fall, α<SUB>ff</SUB>. In order to reach the high level of observed deuteration of {{{N}}}<SUB>2</SUB>{{{H}}}<SUP>+</SUP>, we find that the most likely evolutionary history of the cores involves collapse at a relatively slow rate, ≲ one-tenth of free-fall.STAMPAenArticle10.3847/0004-637X/821/2/942-s2.0-84969716695000377102700023https://iopscience.iop.org/article/10.3847/0004-637X/821/2/942016ApJ...821...94KFIS/05 - ASTRONOMIA E ASTROFISICA