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Can Chemical Maps Indicate the Formation of Methyl Formate? Ashley Barham; Jessica Jones; Jalisa Taylor; Anthony Remijan The Center for Chemistry of the Universe, National Radio Astronomy Observatory Abstract:: Abstract Experiment: Methyl formate (HCOOCH3) is a well known molecule in the interstellar medium; however its formation is not clearly understood (Horn et al.2004). It is presumed that methyl formate is formed in various processes such as, grain chemistry (Garrod and Herbst,2006) and other gas-phase mechanisms (Horn et al. 2004). We propose that methyl formate is formed through a methyl transfer reaction leading to two different geometries of methyl formate, cis- and trans-. There are two consequences of this hypothesis; in the interstellar medium in regions where we find methyl formate, formic acid should be absent. The second consequence is that we should be able to find the cis- and trans- geometries of methyl formate in space. Liu et al. (2002) mapped the distribution of methyl formate and formic acid and showed that there is a clear difference in the locations of the peaks. These observations support the first consequence of our hypothesis. The cis- and transgeometries have also been detected toward the SgrB2N star forming region. Therefore, the next step was to detect these two geometries of methyl formate (cis- and trans-) in the Orion KL region and we attempted this detection using the GBT. There are two consequences of this hypothesis; in the interstellar medium in regions where we find methyl formate, formic acid should be absent. As such, observed contour maps showing the concentrations of methyl formate and formic acid should show a difference in the location of their peaks. The above images show the distributions of both methyl formate and methanol toward the high mass star forming region Orion KL at a distance of 450 pc with the Plateau de Bure interferometer (below). Problem: The data collected from the Orion KL region detected chemical maps of methanol, formic acid, and methyl formate. There was also data of cis- and trans- geometries detections in the Sagittarius B2N region. The problem is being able to detect the cis- and trans- geometries in the Orion KL region. The images show the detections of trans- and cismethyl formate toward the Sagittarius B2N region, using the GBT (right). Introduction: Recent & Future Work: Methyl formate (HCOOCH3) is a well known molecule in the interstellar medium; however its formation is not clearly understood (Horn et al. 2004). It is presumed that methyl formate is formed in various processes such as, grain chemistry (Garrod and Herbst, 2006) and other gas-phase mechanisms (Horn et al. 2004). New eVLA observations show widespread distributions of methyl formate and methanol (see image below). GBT observations show a clear detection of methanol (top spectrum) but no detection of either geometry of methyl formate beyond the 1σ noise limit (~50 mK). More integration time is clearly necessary. The above image (right) shows the distributions of both formic acid (bold contours) and methyl formate (light contours) toward the high mass star forming region Orion KL with the BIMA interferometer (below). These maps show clear evidence in support of our hypothesis. Hypothesis: We propose that methyl formate is formed through a methyl transfer reaction (as seen in equation 1) leading to two different geometries of methyl formate, cis- and trans-. The cis- and trans- geometries of methyl formate refer to the orientation of the methyl group (CH3) with respect to the other atoms in methyl formate. We can detect the difference in these geometries based on the spectroscopy of cis- and trans- as measured in the lab. Methyl Transfer Reaction: [CH3OH2]++ HCOOH------>HC(OH+)OCH References: 1. The Gas-Phase Formation of Methyl Formate in Hot Molecular Cores, Horn et al., 2004, ApJ, 611, 605. 3+H2O 2. Formation of methyl formate and other organic species in the warm-up phase of hot molecular cores, Garrod & Herbst, 2004, A&A, 457, 927. With the increase in concentration of methyl formate and water there should be a decrease of formic Acid and methanol. With formic acid being the limiting reagent in the reaction, there should be little to no formic acid with the presence of methyl formate. Methanol and water are already in high abundance in space, so their detection would not be a sufficient marker with the finding of methyl formate. 3. Unveiling the Chemistry of Hot Protostellar Cores with ALMA- M. Guelin, N. Brouillet, J. Cernicharo, F. Combes, A. Wootten, 2008, A&SS, 313, 45. 4. Observations of Formic Acid in Hot Molecular Cores, L. Sheng-Yuan, D.M. Mehringer, & L.E. Snyder, 2001, ApJ, 552, 654. 5. IRAS16293-2422: Evidence for Infall onto a Counterrotating Protostellar Accretion Disk, Remijan & Hollis, 2006, ApJ, 640, 842. 6. Formic Acid in Orion KL from 1 Millimeter Observations with the Berkeley-IllinoisMaryland Association Array- Liu, Sheng Yuan, Girant, J.M., Remijan, A, & Snyder L.E., 2002, ApJ, 576, 255. The formation of both cis- and trans- geometries are exothermic as the products are lowered in energy than the reactants. While the reaction barrier for cis- is 1500K, the reaction the reaction barrier for trans- is essentially barrier less (-700K) (See figure below). Acknowledgements: The above images show the distributions of both formic acid (blue) and methyl formate (red) toward the low mass star forming region IRAS 16293 with the VLA interferometer (below). Again, this map shows clear evidence in support of our hypothesis. Dr. Brooks H. Pate Dr. Anthony Remijan Dr. Robin Pulliam Dr. Edward Murphy Amanda Steber Dan Zaleski Justin Neill Sara Fitzgerald Matt Muckle Funding: This work was supported in part by the NSF Centers for Chemical Innovation through award CHE-0847919, the University of Virginia and the Virginia-North Carolina Alliance LSAMP Program.