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Abundance and Distribution of the HNCS/HSCN isomer pair In Sagittarius B2 Gilles Adande, Lucy Ziurys, DeWayne Halfen Department of Chemistry, Department.

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Presentation on theme: "Abundance and Distribution of the HNCS/HSCN isomer pair In Sagittarius B2 Gilles Adande, Lucy Ziurys, DeWayne Halfen Department of Chemistry, Department."— Presentation transcript:

1 Abundance and Distribution of the HNCS/HSCN isomer pair In Sagittarius B2 Gilles Adande, Lucy Ziurys, DeWayne Halfen Department of Chemistry, Department of Astronomy, Steward Observatory and Arizona Radio Observatory, University of Arizona The chemical physics program, Departments of Chemistry, Astronomy and Physics, The Ohio State University, Columbus Donghui Quan, Eric Herbst

2 metastable isomers E (cm -1 ) HNCS HSCN ISM convenient “laboratory” for transient species Understanding interstellar chemistry formation pathways, branching ratios etc… Tracers of ISM physical conditions HNCO/HOCN in cold gas Large organic molecules only in hot cores What about HNCS/HSCN ?

3 ARO 12 m ALMA type Band 3 receiver ( GHz) 3 mm low (68-90 GHz) 12 m at Kitt Peak SpeciesFrequency (MHz) Transition J′ Ka′,Kc′  J Ka,Kc Sgr B2 HSCN ,8  7 0, ,9  8 0,8 HNCS ,8  7 0, ,9  8 0,8 TMC-1 HSCN ,7  6 0, ,8  7 0,7 HNCS ,7  6 0, ,8  7 0,8

4 Mapping Observations of Sgr B2 n(H 2 ) ~ 10 5 cm -3 T ~ K ~ 15 pc n(H 2 ) < 10 4 cm -3 T < 20 K Hot cores n(H 2 ) ~ 10 7 cm -3 T ~ K Hot ring T ~ K Approximate beam size ~ 1’ Sgr B2 (M)

5 Δα ( arcmin) Δδ (arcmin ) HNCS: J = 8 0,8  7 0,7 Sgr B2 CCS

6 Δα ( arcmin) Δδ (arcmin ) HSCN: J = 8 0,8  7 0,7 Sgr B2

7 9 0,9  8 0,8 Extended emission Not hot core molecule Consistent lineshapes Gas phase processes major contribution

8 HSCN HNCS

9 HSCN: 1.2×10 12 – 1.3×10 13 cm -2 across the cloud HNCS: 6.3×10 12 – 4.3×10 13 cm -2 LTE approximation Optically thin T rot = 20 K Average abundance of 2 transitions consistent to 10% Abundances

10  HNCS/HSCN Sgr B HNCS/HSCN ratio ~ across Sgr B2 Smaller toward hot cores Higher in the envelope

11 Observations in TMC-1 Kaifu et al, 2004

12 HNCS ~ 1.3 HSCN Column density ~ 7 – 8 × cm -2 HNCS/HSCN ratio T ~ 10K 1 st detection of HNCS in dark clouds

13 Formation of HNCS/HSCN ? HNCS + + H 2  HNCSH + / H 2 NCS + + H NCS + + H 2  HNCS + + H HNCSH + + e -  HNCS / HSCN + H H 2 NCS + + e -  HNCS + H Gas Phase ion-molecule formation Accretion on grains NCS H H HNCS HSCN Thermal + non thermal desorption Destruction with ions and neutrals

14 Detailed gas-grain model 3 phase model: warm envelope of hot cores 1 phase model: cold clouds, cold halo

15 Conclusions In Sgr B2 Extended, consistent HNCS and HSCN emission HNCS/HSCN ~ 1 near hot cores HNCS/HSCN up to 10 in moderately dense gas In TMC-1 HNCS/HSCN ~ 1 in dark clouds Gas phase process major contribution Possible gas grain influence HNCSH +, reaction rate etc… await measurement

16 Acknowledgements Professor Lucy Ziurys Dr. DeWayne Halfen Dr. Donghui Quan Professor Eric Herbst Dr. Emmy Tenenbaum, Lindsay Zack, Jessica Dodd, Ming Sun Matthew Bucchino, Jie Min, Robin Pulliam, Brent Harris Funding: NASA-NSF


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