DEUTERATED MOLECULES IN TRANSLUCENT AND DARK CLOUDS

摘要: We present observations of 10 deuterated molecular species in the dark clouds TMC-1, L183, and translucent object CB 17, as well a subset other objects. With sensitive TMCNH 3 J \ 1¨0 2¨1 transitions DCN, DNC, we have been able to derive N 2 D‘, constants that include complex nuclear quadrupole hyper—ne splitting these species, which is essential determine accurate abundances. The spectroscopic results required, turn, new radiative transport techniques handle eUects. Our abundance determinations also utilize secondary isotopomers involving 13C, 18O, 15N. Compared with earlier D/H ratios literature, innovations resulted radically diUerent values some cases TMC-1 TMC-1; DCN/HCN 17), (N D‘/N H‘ ;N H D/NH important modi—cations others TMC-1). usually produce (C HD/C deuteration lower than those obtained by simpler methods. Thus, addition special noted above, our are generally previous ones factors typically 2. —nd occurs only regions high density, while nondeuterated reside at densities. A recently proposed model low-density objects containing embedded small, high-density fragments explains observations. To study chemistry used New Standard Model, modi—ed all monodeuterated now 9930 reactions 610 species. models explore dependence upon temperature, ionization rate, extinction, epoch, elemental Within uncertainties, agreement between observed modeled for nearly sources. agree Roberts & Millar recent, similar study. signi—cantly higher L183 TMC, intermediate 17. general, however, believe ii normal ˇˇ cold cloud, 17 typical slightly warmer object, TMC region perhaps underdeuterated certainly strongly so case These NH . anomalous no plausible single explanation terms gas-phase this time. Grain processes implicated. ..