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 Donghui Quan, Eric Herbst The chemical physics program, Departments of Chemistry, Astronomy and Physics, The Ohio State University, Columbus

metastable isomers • ISM convenient “laboratory” for transient species E (cm-1) 21825 • ISM convenient “laboratory” for transient species • Understanding interstellar chemistry formation pathways, branching ratios etc… • Tracers of ISM physical conditions HSCN 4127 HNCS • HNCO/HOCN in cold gas • Large organic molecules only in hot cores • What about HNCS/HSCN ?

ARO 12 m 12 m at Kitt Peak • ALMA type Band 3 receiver (84-116 GHz) Species Frequency (MHz) Transition J′Ka′,Kc′  JKa,Kc Sgr B2 HSCN 91750.63 80,8  70,7 103217.47 90,9  80,8 HNCS 93830.05 105558.07 TMC-1 80283.16 70,7  60,6 82101.80 80,8  70,8 12 m at Kitt Peak • ALMA type Band 3 receiver (84-116 GHz) • 3 mm low (68-90 GHz)

Mapping Observations of Sgr B2 Hot cores n(H2) < 104 cm-3 T < 20 K n(H2) ~ 107 cm-3 T ~ 150-300 K ~ 15 pc Approximate beam size ~ 1’ Sgr B2 (M) n(H2) ~ 105 cm-3 T ~ 20-80 K Hot ring T ~ 100-120 K

HNCS: J = 80,8  70,7 Sgr B2 CCS Δδ (arcmin) Δα (arcmin)

HSCN: J = 80,8  70,7 Sgr B2 Δδ (arcmin) Δα (arcmin)

• Consistent lineshapes 90,9  80,8 • Extended emission • Not hot core molecule • Consistent lineshapes • Gas phase processes major contribution

HNCS HSCN

Abundances • LTE approximation • Optically thin • Trot = 20 K • Average abundance of 2 transitions consistent to 10% HSCN: 1.2×1012 – 1.3×1013 cm-2 across the cloud HNCS: 6.3×1012 – 4.3×1013 cm-2

HNCS/HSCN ratio • ~ 1.7 - 10.1 across Sgr B2 Da Dd HNCS/HSCN Sgr B2 1 -2 4.9 3.7 -1 5.3 3.5 2.6 4.6 3.3 2.5 3.1 1.7 2.8 3.4 2 8.5 5.8 5.9 3 10.1 7.3 HNCS/HSCN ratio • ~ 1.7 - 10.1 across Sgr B2 • Smaller toward hot cores • Higher in the envelope

Observations in TMC-1 Kaifu et al, 2004

• 1st detection of HNCS in dark clouds • T ~ 10K • Column density ~ 7 – 8 × 1011 cm-2 • HNCS/HSCN ratio HNCS ~ 1.3 HSCN

HNCSH+ + e-  HNCS / HSCN + H Formation of HNCS/HSCN ? • Accretion on grains • Gas Phase ion-molecule formation NCS+ + H2  HNCS+ + H H H HNCS+ + H2  HNCSH+ / H2NCS+ + H NCS HNCSH+ + e-  HNCS / HSCN + H HSCN HNCS H2NCS+ + e-  HNCS + H Thermal + non thermal desorption • Destruction with ions and neutrals

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

Conclusions • In Sgr B2 • In TMC-1 • 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

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