title: HCl absorption toward Sagittarius B2.
abstract: We have detected the 626 GHz J = 1 --> 0 transition of hydrogen chloride (H35Cl) in absorption against the dust continuum emission of the molecular cloud Sagittarius B2.  The observed line shape is consistent with the blending of the three hyperfine components of this transition by the velocity profile of Sgr B2 observed in other species.  The apparent optical depth of the line is tau approximately 1, and the minimum HCl column density is 1.6 x 10(14) cm-2.  A detailed radiative transfer model was constructed which includes collisional and radiative excitation, absorption and emission by dust, and the radial variation of temperature and density.  Good agreement between the model and the data is obtained for HCl/H2 approximately 1.1 x 10(-9).  Comparison of this result to chemical models indicates that the depletion factor of gas-phase chlorine is between 50-180 in the molecular envelope surrounding the SgrB2(N) and (M) dust cores.
authors.affiliation: Division of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena 91125, USA.
authors.forename: J
authors.initials: J
authors.lastname: Zmuidzinas
authors.forename: G A
authors.initials: GA
authors.lastname: Blake
authors.forename: J
authors.initials: J
authors.lastname: Carlstrom
authors.forename: J
authors.initials: J
authors.lastname: Keene
authors.forename: D
authors.initials: D
authors.lastname: Miller
mesh_terms: D055580:Astronomical Phenomena; D001256:Astronomy; D002713:Chlorine / Q000737:chemistry*; D004391:Dust / Q000032:analysis*; D004735:Energy Transfer; D005118:Extraterrestrial Environment; D006851:Hydrochloric Acid / Q000032:analysis*; D008956:Models, Chemical; D008962:Models, Theoretical; D016082:Solar System; D013054:Spectrophotometry, Atomic; D013057:Spectrum Analysis
chemical_list: D004391:Dust; D002713:Chlorine; D006851:Hydrochloric Acid