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\title{Nitrile Chemistry in Sgr B2(N)}
\author{Joanna Corby \thanks{University of Virginia}
\and{Anthony Remijan \thanks{National Radio Astronomy Observatory}}
\and{Brooks Pate \thanks{University of Virginia}} 
\and{Robin Pulliam \thanks{National Radio Astronomy Observatory}}}

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\maketitle

\begin{abstract}
Haven't yet put together the abstract.

\end{abstract}

\newcommand{\arcs}{\mbox{\ensuremath{.\!\!^{\prime\prime}}}} % fractional arcsecond symbol: 0.''0

\section{Scientific Justification}

       The high mass star forming region Sgr B2(N) is perhaps the most molecule-rich interstellar environment observable within our Galaxy.  For this reason among others, it has received much observational attention by the astrochemistry community. Of all the molecules detected in astronomical environments, more than half have been detected toward SgrB2(N) first   Various complex molecules, including but not limited too CH3OH, CH3CH2CN, CH2CHCN, CH3CN, CH3OCHO, CH3COOH and HCOOH (DO A LIT SEARCH ON REMIJAN or SNYDER or Y. J. KUAN or S. Y. LIU, or MEHRINGER) have been detected by single dish observations and imaged by millimeter interferometers, mostly at low spatial and spectral resolution.  Yet, relatively few molecules have been imaged with the high angular resolution available with the VLA.
  
       Ethyl cyanide ($CH_{3}CH_{2}CN$) is among the few complex molecules that have been imaged at high angular resolution in Sgr B2(N) with the VLA. Hollis et al (2003) imaged the 43 GHz J=7 $\rightarrow$ 6 line of ethyl cyanide using the DnC configuration and determined three spatially distinct ethyl cyanide peaks, two in emission and a third in absorption.  In addition, each peak has a unique velocity within the SgrB2N region.  The ethyl cyanide emission regions are located toward the "Large Molecular Heimat" (LMH) (Snyder \& Miao 1997?) (coincident with the HII region K2) (reference) and in a region $\sim 5 \arcsec$ north of the LMH at a location coincident with the quasi-thermal methanol emission core ("h") (reference).  The ethyl cyanide absorption region is located $\sim 10"$ NE of the LMH peak, which we will hereafter refer to as the "NE absorption region".  The NE absorption region also contains an HII emission peak, K6 (reference).  The resulting map of ethyl cyanide emission and absorption from Hollis et al.\ 2003 is shown in Figure 1a. Emission features are shown in solid contours, and the absorption features are shown in dashed contours.  In addition, the ethyl cyanide absorption region is located just inside an ionization front (Ionization Front Author, et al. 2000?), which is labelled in Fig 1b. 
 
       Given the velocity structure of ethyl cyanide features resolved by the VLA observations, comparable single dish spectra toward the  Sgr B2(N) pointing position should contain both emission and absorption line profiles of ethyl cyanide separated by the velocity components measured by Hollis et al.\ 2003.  The high signal-to-noise (noise $\approx 1 mK$), high spectral resolution ($64.4kHz$) single dish data available through the PRIMOS Survey conducted on the Green Bank Telescope show this velocity structure (Remijan et al. BAAS, 2008? and available at www.cv.nrao.edu/~aremijan/PRIMOS).  In addition to ethyl cyanide, acetonitrile ($CH_{3}CN$) and cyanoacetylene ($HCCCN$) similarly have both absorption and emission features, and other nitriles, including vinyl cyanide ($CH_{2}CHCN$), cyanomethyl ($CH_{2}CN$), cyanoallene ($H_{2}CCCHCN$), and methyl isocyanide ($CH_{3}NC$), appear only in absorption.  (** WE DO NOT HAVE DETECTIONS OF CYANOALLENE IN SGRB2N.  IM SURE WE HAVE CH2CN BUT PERHAPS NOT BETWEEN 18-20 GHZ.)  Examples of the complex emission and absorption features due to the combination of hyperfine splitting and multiple velocity components toward the SgrB2N region associated with acetonitrile and cyanoacetylene are shown in Figure 2.  Given the distinct regions responsible for the ethyl cyanide emission and absorption features identified by Hollis et al.\ (2003), we expect the nitrile absorption features to be primarily associated with the NE absorption region, placing the nitrile species in a coincident region and indicating the possibility of common chemical pathway.  

      The velocity structure of the absorption and emission features seen in the transitions of nitriles detected by the GBT become particularly interesting in light of recent laboratory results obtained at the University of Virginia.  Acetonitrile and hydrogen sulfide (H2S) were exposed to electron bombardment via a 1600V discharge nozzle (McCarthy et al. 2000??) generating unanticipated rich results.  The bombardment produced 22 molecular species, of which 16 are confirmed astronomical species.  Figure 3 lists some of the product species and indicates interstellar species with an asterisk.  The identified species constitute 13$%$ of all confirmed astronomical molecules.  The lab spectra also include approximately 200 unidentified lines, some of which correspond to unidentified lines in PRIMOS data on Sgr B2(N).  An example of an unidentified transition in the GBT data and lab data are shown in Figure 4.  What is even more interesting is that the measured abundance ratios of molecules detected in the lab experiment are in qualitative agreement with abundance estimates obtained using the GBT PRIMOS line data.  Table 1 provides lab abundance ratios and Sgr B2(N) abundance ratio estimates of nine species.

      The laboratory results suggest the possibility of an electron bombardment scenario for the formation of nitrile species in Sgr B2(N).  The results presented by Hollis et al.\ (2003) support this hypothesis because there is indication of a region rich in nitriles (at least ethyl cyanide) inside an arc-shaped ionization front.  In the laboratory, the mechanism by which acetonitrile and hydrogen sulfide react to form 22 distinct molecular species includes radical-radical reactions involving cyanomethyl ($CH_{2}CN$).  The electron bombardment of acetonitrile produces the cyanomethyl radical, which then immediately reacts with other radicals to form more complex species.  This key species, which is also detected in absorption in Sgr B2(N), may place it spatially coincident with the other nitriles and as such, would support our hypthesis.  Finally, extension of this theory would place all the other nitriles detected with absorption features also in the same location.

       We propose a test of the electron bombardment scenario in the NE absorption region via spectral line imaging of nitriles  with the EVLA.  Very few astrochemical investigations are motivated by direct lab results as ours.  As such, we are applying a new model for astrochemical searches whereby direct laboratory measurements provide a testable hypothesis that can be followed on directly by astronomical observations. Though the astronomical molecular inventory currently stands at $\sim$ 169 detected species and their isotopologues, the formation mechanisms of even the simplest molecular species are not well understood.  In previous efforts, searches for interstellar species have taken place with with little understanding and usually no motication of obtaining information on chemical formation pathways.  As such, we are presenting a new methodology for obtaining fundamental information on the chemical reaction dynamics within an astronomical environment that is directly motivated by laboratory results.  In addition to the valuable information for chemical formation scenarios, our observations will also help constrain the dynamics and kinematics toward the NE region of SgrB2N containing the NE absorption region, the associated ionization front, and ionizing source(s).

\section{Technical justification}


      We propose to image the region of Sgr B2(N) containing the NE absorption region and the LMH emission peak with the EVLA in the K band.  Single dish K band data on Sgr B2(N) are available from PRIMOS, allowing for comparison (make this more powerful?).  We will set a 2 GHz window from 18.5 to 20.5 GHz, to image (how many) lines of cyano methyl, methyl cyanide, ethyl cyanide, vinyl cyanide, cyanoallene, methyl isocyanide, ~ethene isocyanide (blended in GBT), and cyanoacetylene that were present in the PRIMOS Survey.  With the high sensitivity of the DnC configuration, we expect to see additional lines from these and other nitrile species that were below the sensitivity limit of the Primos Survey.  With ~13 hours of integration time (GOT THIS FROM EVLA EXPOSURE CALCULATOR--CHECK THIS), we can achieve an RMS noise of .5K, compared to PRIMOS noise of 1K, allowing for identification of very weak lines.  The spatial resolution available through the EVLA ($\theta\sim2 \arcs 8$) will allow us to determine the spatial distribution of these species, providing the first observational test of a lab-driven electron bombardment hypothesis for nitrile chemistry in the NE abs region.
%.... I'm sure there is more to say in the Technical Justification. 

%(I feel like Justin should be an author bc of his work from the powerpoint.)



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