DANIEL P. ZALESKI, JUSTIN L. NEILL, MATT T. MUCKLE, AMANDA L. STEBER, RYAN A. LOOMIS, BRENT J. HARRIS, and BROOKS H. PATE Department of Chemistry, University of Virginia, McCormick Rd, Charlottesville, VA ,USA. JOANNA F. CORBY Department of Astronomy, University of Virginia, McCormick Rd, Charlottesville, VA 22904, USA. ANTHONY J. REMIJAN National Radio Astronomy Observatory, 520 Edgemont Rd., Charlottesville, VA VALERIO LATTANZI and MICHAEL C. MCCARTHY Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, and School of Engineering & Applied Sciences, Harvard University, 29 Oxford St., Cambridge MA Nitrile Chemistry: Comparison of Laboratory Reaction Chemistry and Interstellar Observations The Ohio State 66 th International Symposium on Molecular Spectroscopy, June 22 nd, 2011.

Advances in Radio Astronomy  The next-generation radio telescope arrays (ALMA and EVLA) will provide high spatial resolution observations of chemical species that will uncover new insights into chemical reaction processes.  The broadband capabilities of ALMA and EVLA make it possible to observe the overall chemical composition of different spatially resolved interstellar environments rather than traditional methods of mapping a single transition of a single molecular species.  This information about local chemical composition provides more stringent tests of reaction chemistry hypotheses.  There are lab-based broadband techniques in place suitable for screening broadband interstellar data

New Strategy  Get away from: think of a molecule, go look for it in the ISM  Propose: screen reaction chemistry, deep average and drive the sensitivity way up, then analyze the reaction mixture  Identify known molecules using databases like Splatalogue.net  Then identify molecules based on related chemistry and quantum mechanics  Screen the unassigned transitions vs broadband interstellar data  If there are matches, put the effort into determining those molecular carriers  Does this strategy pay off?

A Reactions Approach to Interstellar Chemistry  Nitriles have high dipole moments allowing for greater chance of interstellar detection.  Nitriles (and isonitriles) are the largest class of known interstellar molecules.  Isomer ratios are a potential test of proposed formation mechanisms.  Pulsed discharge nozzles have had great success in producing interstellar species - possible indication of common chemistry.  Start with high abundance species and identify reaction products: CH 3 CN + H 2 S  CH 2 CN + CH 3 + CN + SH + S + H  products  Is there support for similar reaction chemistry in the interstellar medium?

Experiment Gordon G. Brown, Brian C. Dian, Kevin O. Douglass, Scott M. Geyer, Steven T. Shipman, and Brooks H. Pate. Rev. Sci. Instrum. 79, , (2008). M.C. McCarthy, W. Chen, M.J. Travers, and P. Thaddeus, Ap. J. Supp. Series, 129, (2000). x3 No Helmholtz coil 24 Gs/s AWG

Broadband rotational spectrum of H 2 S and CH 3 CN The signal level shown in the red spectrum is about 40x weaker than the 13 C level of the starting material CH 3 CN x4000 x600

Laboratory Reaction Chemistry  The chemical composition produced from the pulsed discharge suggests the main processes are: - Radical Formation (directly detected or inferred) - Radical Recombination followed by H 2 loss and/or isomerization  24 molecules have been identified in the laboratory spectrum, 18 are interstellar  Accounts for ~10% of all known interstellar molecules without intentionally adding oxygen - O-bearing species likely resulting from atmospheric H 2 O in the line  Still hundreds of unassigned laboratory transitions - Over 50% of the remaining lines Molecule Number Atoms Interstellar SH2Y SSH3N NCS3N SO 2 3Y OCS3Y HSCN4Y HNCS4Y HCNS4N H 2 CS4Y CCCS4Y HCCCN5Y HCCNC5Y CH 2 CN5Y H 2 CCS5N HCSCN5N CH 3 NC6Y CH 3 SH6Y H 2 CCNH6Y CH 2 CHCN7Y CH 2 CHNC7N HSCH 2 CN7N CH 3 CCH7Y CH 3 CCCN8Y H 2 CCCHCN8Y CH 3 CH 2 CN9Y

Dehydrogenation ∙CH 3 + ∙CH 2 CN  CH 3 CH 2 CN -421 kJ/mol CH 3 CH 2 CN  CH 2 CHCN + H kJ/mol CH 2 CHCN  HCCCN + H kJ/mol CH 3 CH 2 CN  HCCCN + 2H kJ/mol The energy released by the radical combination reaction could potentially be enough to sequentially dehydrogenate.

New Lab Detections Predicted From This Chemistry SH + CH 2 CN  HSCH 2 CN -313 kJ/mol HSCH 2 CN  HCSCN + H kJ/mol MP2/6-31+G(d,p)

HCSCN Spectral Parameters EXPB3LYP/6-31G A (MHz) (15) B (MHz) (37) C (MHz) (37) ΔJ (kHz)1.145(30)1.067 ΔJK (kHz) (47) δJ (kHz)0.216(31) Xaa (MHz)-5.291(51) 0.25(Xbb-Xcc) (MHz)-0.483(41) 22 lines 17 kHz M. Bogey et al. J. Am. Chem. Soc., 111, (1989), Previous room temperature mm-wave study

ISM Analysis from PRIMOS Molecule Column Density (cm -2 ) Rotational Temperature (K) HCCCN~6* *6* CH 2 CHCN~10* * CH 3 CH 2 CN~2* * CH 2 CN~ † Numerous product species present from our experiment, including CH 2 CHCN, CH 3 CH 2 CN, HC 3 N and CH 2 CN. Common spectral features (absorption in the 18 GHz range) and evidence for a low-temperature velocity component (64 km/s and 82 km/s, 73 km/s warmer). Cold rotational temperatures do not suggest thermal desorption from grains. If this chemistry is occurring in Sgr B2(N), we expect that product molecules will be co-spatial and rotationally cold. * 64 km/s † 68 km/s

Spatial Maps CH 3 CH 2 CN - VLA in DnC around 43.5 GHz toward the Sgr B2(N) Solid contours – emission Dashed contours - absorption Color scale - continuum emission around 43.5 GHz Unusual position for nitrile rich chemistry? J.M. Hollis et al., ApJ, 596, L235-L238, (2003)

Common Lineshapes Definitely not the conventional 3 velocity components

(Z)-Ethanimine – CH 3 CHCNH R. D. Brown, P. D. Godfrey, and D. A. Winkler. Aust. J. Chem. 33, (1980), 1-7.

(Z)-Ethanimine

(E)-Ethanimine

Conclusions  The current testable hypothesis is that these species may have a similar formation chemistry in regions toward Sgr B2(N).  Broadband reaction screening of interstellar molecules  Screen for chemical processes  Identified 2 new molecules by rotational spectroscopy (HSCH 2 CN and HCSCN) - Not including previously reported HSCN isomers  Because of the discharge bias to synthesize interstellar species, these are potential candidates for interstellar detection, even though they don’t appear in the PRIMOS data  25 molecules detected in discharge, 19 interstellar

Cont.  Emergence of broadband techniques in the lab and interstellar observations  Determine molecules coupled by reaction chemistry  Family of molecules in the lab and the ISM in absorption  Once ALMA/EVLA are on, double screen broadband laboratory data with broadband interstellar data  Shown that this approach is fruitful: (Z)-ethanimine and (E)-ethanime

Acknowledgments Centers for Chemical Innovation Award Number

Isomerization: Isonitriles and Hydride Shifts CH 2 CHCN → CH 2 CHNC HCCCN → HCCNC CH 3 CN ←→ CH 2 CNH ∆E a 273 kJ/mol Energy ∆E a 74 kJ/mol ↓ - H kJ/mol J. B. Moffat. J. Phys. Chem. 81, No. 1 (1977), X. Yang, S. Maeda, K. Ohno. Chem. Phys. Lett. 418, (2006), A. Doughty, G. B. Bacskay, and J. C. Mackle. J. Phys. Chem. 98, (1994), MP2/6-31+G(d,p)

Rough HSCH 2 CN Spectral Parameters EXPM062X/ G(d,p) A (MHz) B (MHz) C (MHz) Xaa (MHz) (Xbb-X) (MHz) lines 68 kHz Fitting 1 state

Pyrolysis K. D. King and R. D. Goddard. J. Phys. Chem., 82, (1978), kT(1000K) = ~8 kJ/mol Recall: CH 3 ∙ + CH 2 CN∙  CH 3 CH 2 CN yielded 421 kJ/mol Key intermediate to detect c c