The Interstellar Detection of HSCN in Sgr B2(N) DeWayne T. Halfen, L. M. Ziurys Departments of Chemistry and Astronomy, Steward Observatory, Arizona Radio Observatory, University of Arizona M. C. McCarthy, C. Gottlieb, P. Thaddeus Harvard-Smithsonian Center for Astrophysics, and School of Engineering & Applied Sciences, Harvard University June 24, 2010

Isomer Chemistry in the ISM Some isomer pairs now found in the interstellar medium (ISM) By examining isomer ratio, insight into formation mechanism HCN and HNC found in many dense molecular clouds and circumstellar envelopes (Hirota et al. 1998; Ziurys & Turner 1986) HNC – 5600 K higher in energy than HCN Yet HNC/HCN isomer ratio ranges from 0.014 – 4.4 Both species created via electronic recombination of HCNH+ Larger isomers also observed Methyl formate, acetic acid, glycolaldehyde (C2H4O2) Methyl formate dominant species, but unclear three species formed by common mechanism

HNCS and HSCN Isomers HNCS known, abundant interstellar molecule Detected by Frerking et al. (1979) towards Sgr B2(OH) HSCN metastable isomer of HNCS Lies 3000 K higher in energy than HNCS Rotational spectrum of HSCN recently measured in Harvard laboratory (Brünken et al. 2009) 18 transitions recorded from 10-350 GHz

Astronomical Search for HSCN Spectrum of HSCN searched for towards Sgr B2(N) Giant molecular cloud near center of the Milky Way Examined our spectral-line survey data taken with the Arizona Radio Observatory (ARO) 12m on Kitt Peak Observations at 2 and 3 mm (65-180 GHz) HNCS transitions also studied for comparison KP 12m

3 mm data taken with ALMA Band 3 receiver (84-116 GHz) Uses new ALMA-type sideband-separating (2SB) mixers Order of magnitude improvement in receiver sensitivity, bandwidth, and stability Raw data only need simple baseline taken out RAW data HSCN ALMA Band 3 mixer

Eight transitions of HSCN detected towards Sgr B2(N) Almost linear species: only Ka = 0 transitions are strong, favorable lines Eight transitions of HSCN detected towards Sgr B2(N) H C N S H C N S

5 clean transitions, 1 blended, 2 contaminated HSCN Sgr B2(N) HSCN Sgr B2(N) Eight transitions of HSCN observed 5 clean transitions, 3 others contaminated Halfen et al. 2009 5 clean transitions, 1 blended, 2 contaminated

6 transitions of HNCS also present in survey HNCS Sgr B2(N) 6 transitions of HNCS also present in survey 2 clean lines, rest blended with emission from other species Lines from HNCO, HOCN also detected Source velocity and line width consistent with HSCN and HNCS HNCS

Intensities from 50-110 mK, consistent VLSR, DV1/2 Freq. (MHz) J′Ka,Kc  J″Ka,Kc Eu(K) qb(″) TR*(K) DV1/2(km/s) VLSR(km/s) Comment HSCN 68815.15 60,6  50,5 11.5 91 0.069 ± 0.014 23.5 ± 4.4 69.7 ± 4.4 Good match 80283.17 70,7  60,6 15.4 78 0.073 ± 0.006 20.1 ± 3.7 64.8 ± 3.7 91750.63 80,8  70,7 19.8 68 0.109 ± 0.003 16.1 ± 3.3 66.6 ± 3.3 103217.47 90,9  80,8 24.7 61 0.063 ± 0.004 19.6 ± 2.9 66.3 ± 2.9 114683.62 100,10  90,9 30.2 55 0.074 ± 0.007 20.5 ± 2.6 67.2 ± 2.6 137613.49 120,12  110,11 42.9 46 0.050 ± 0.004 20.0b 66.0b Partially Resolved 149077.07 130,13  120,12 50.1 42 ~0.07 No discernible peak 160539.63 140,14  130,13 57.8 39 HNCS 82101.82 15.7 77 ~0.08 Blended with HC3N 93830.05 20.2 67 0.077 ± 0.003 17.8 ± 3.2 68.3 ± 3.2 105558.07 25.3 60 0.114 ± 0.003 20.4 ± 2.8 63.8 ± 2.8 140740.38 43.9 45 ~0.04 Edge of 0.10 K line 152467.13 51.2 41 ~0.09 Edge of 0.13 K line 164193.53 59.1 38 … Contaminated Intensities from 50-110 mK, consistent VLSR, DV1/2

f(X/H2) = 1.1 x 10-11 f(X/H2) = 4.5 x 10-12

HNCSH+ + e-  HNCS or HSCN + H Formation in Sgr B2(N) Self-consistent data set taken with same telescope Compare the chemistry of HNCS and HSCN HSCN only factor of 3 less abundant Samples cold gas in this region Both formed in cold gas via ion-molecule chemistry from a common precursor: HNCSH+ HNCSH+ + e-  HNCS or HSCN + H Not formed on grains or through shocks HNCSH+ not yet studied in laboratory

Comparison to HNCO and HOCN Spectra of HNCO and HOCN also present in Sgr B2(N) data HOCN lies 12,300 K above HNCO HNCO: f(X/H2) = 5.7 x 10-10 HOCN: f(X/H2) = 3.2 x 10-12 HNCO/HOCN = 180 Formed from HNCOH+ / H2NCO+ ? O/S ratio ~ 10 from NO/NS, CH3OH/CH3SH, H2CO/H2CS HNCO/HNCS = 52 Suggests the ratio is due to formation mechanism, not overall ratio in Sgr B2(N)

Future Directions Conducted mapping observations across Sgr B2 and searched for HNCS and HSCN in TMC-1 (see RF02) Search for these species in cold and warm sources Confirm formation mechanism

Acknowledgements Ziurys Group Harvard Group NSF CCI