OBSERVATIONS OF INTERSTELLAR HYDROGEN FLUORIDE AND HYDROGEN CHLORIDE IN THE GALAXY Raquel R. Monje Darek C. Lis, Thomas Phillips, Paul F. Goldsmith Martin Emprechtinger, David Neufeld and Maryvonne Gerin

Fluorine, with IP > IP(H), D 0 (HX) > D 0 (H 2 ). Fluorine is predominantly neutral in the diffuse ISM, and can react exothermically with H 2 and HF. Chlorine, with IP D 0 (H 2 ). Chlorine is predominantly ionized in atomic clouds. Cl + can react exothermically with H 2 to form HCl + The Unique Thermochemistry of Fluorine and Chlorine

Once ionized Cl + reacts with molecular hydrogen exothermically to form HCl +, a process that initiates the chemical reactions of chlorine. In cloud interiors, atomic chlorine is mostly neutral, not ionized, so that the reaction of Cl and H 3 + drives the formation of H 2 Cl +, which then reacts with CO and H 2 O leading to the formation of HCl. An alternative direct route to HCl in either hot gas or regions where vibrationally excited H 2 is abundant is the Cl+H 2 ->HCl+H reaction. The destruction of HCl is dominated both by photoionization and photodissociation and by reactions with C + and H 3 +. The HCl Chemistry

SourceD (kpc) W49N11.5 W31C4.8 SgrA(+50 km/s cloud)8.6 W28A3.8 G W517 W33A4 DR21(OH)1.0

 = 10”, T ex =40K, N tot = 3.0 x cm -2,  V=4 km/s, V LSR =-4km/s [H 35 Cl/H 37 Cl] ratio of 2.7 (3.1 the solar isotopic abundance) Results from an initial LTE model: HCl toward DR21(OH) Intensity ration of 2.7:3:2 (Optically thin 1:2:3) (Optically thick 1:1:1)

HCl toward W31C self absorption feature at VLSR =-1 km/s Absorption by foreground in the V LSR range km/s Neufeld et al, 2010, 518,L108

HCl toward W31C: The Foreground HFS fit + subtraction of absorption Decomposition of the Hyperfine components Courtesy of B. Godard’s Code V LSR N(HCl)HCl/H 2 a x x – x x x x a H 2 column densities derived from CH observations, Gerin et al. 2010, assuming N(CH) = 3.5x10 -8 N(H 2 ).

HCl toward W49N Self absorption from the envelope Outflows? Emission from other lines?

HCl toward SgrA+50 km/s cloud Hyperfine decomposition N tot = 7.17 x cm -2 [H 35 Cl/H 37 Cl] ratio of 2.66

HCl toward W33A

Fluorine is the only atom that can react exothermically with H 2 to form a diatomic hydride: HF is destroyed very slowly by means of cosmic ray-induced photodissociation and as a result of reactions with species of low abundances such as He +,H 3 +, and C +. HF is expected to be the dominant reservoir of gas-phase fluorine. N(HF)/N(H 2 ) ~ 3.6 x HF may be used as a valuable surrogate tracer for molecular hydrogen within diffuse interstellar medium, both in the Milky Way and other galaxies. F + H 2 → HF + H +1.4eV HF in the ISM

NGC 6634 I W51 W49 W31C Orion KL Sgr B2(M) Sgr A+50 NGC 6334I Sgr B2(N)

Sgr A+50 km/s Sgr B2(M) Toward the Galactic center Monje et al. 2011, Apj, 734, L23Sonnentrucker et al. in preparation

ObjectV LSR km s -1 N(HF) x cm -2 HF/H 2 x Sgr B2(M) a -115 – – – – – W49N b 30 – – – W51 b 0 – – – – > G34 b 3 – – – Estimates of the HF/H 2 ratio a H 2 column densities derived from 13 CO assuming CO abundances of 3x10 -5 N(H 2 ) (Sonnentucker 2005). b H 2 column densities derived from CH observations, Gerin et al. 2010, assuming N(CH) = 3.5x10 -8 N(H 2 ).

Conclusions Observations of H 35 Cl and H 37 Cl, and accurate measurements of the 35 Cl/ 37 Cl ratio in different environments, will provide some insight into the chemical evolution of both isotopes, thus into Galactic chemical evolution. Firs detection of HCl in diffuse medium toward the line-of-sight of W31C. One key result from Herschel/HIFI is the ubiquitous nature of hydrogen fluoride within the interstellar medium of the Milky Way. The HF abundances of 1-2 x under a wide variety of interstellar conditions are consistent with the chemical models. HF shows good promise as a tracer of H 2.

HCl is the most abundant Cl-bearing molecule in dense clouds. Both 35CL and 37CL nuclei are believed to form in the last burning stages of massive stars (>10M sun ) and by means of “explosive nucleosynthesis” during supernovae detonation. Observations of H35Cl and H37Cl, and accurate measurements of the 35Cl/37Cl ratio in different environments, can provide some insight into the chemical evolution of both isotopes, thus into Galactic chemical evolution HCl in the ISM

Neufeld et al. 1997, 488, L141 HF in the ISM - A brief history - First detection of interstellar HF J 2-1. Towards Sgr B2 using LWS on ISO. HF abundances of ~ 3 x ISO

Extraordinary Source: Orion KL HF/H lower limit ~ 1.6 x Phillips et al. 2010, A&A, 518, 109

Extragalactic HF van der Werf et al. 2010, A&A, 518, L42 Mrk 231 with SPIRE Mrk 231 with SPIRE HF J = 1-0 detection with the CSO with after ~10hr Monje, Phillips, Peng et al. in preparation Cloverleaf: QSO at z = 2.56 Cloverleaf: QSO at z = 2.56