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

AbstractAbstract::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 trans-

geometries 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.

Methyl formate (HCOOCH3) is a well

known molecule in the interstellar

medium; however its formation is not

clearly understood (Horn et al. 2004). It

Introduction:Introduction:

Experiment:Experiment: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:Problem:

Recent & Future Work:Recent & Future Work:

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 cis-

methyl formate

toward the

Sagittarius B2N

region, using the

GBT (right).

New eVLA observations show widespread

distributions of methyl formate and methanol

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.

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.

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).

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).

References:References:

1. The Gas-Phase Formation of Methyl Formate in Hot Molecular Cores, Horn et al., 2004, ApJ, 611, 605.

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. 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-Illinois-

Maryland Association Array- Liu, Sheng Yuan, Girant, J.M., Remijan, A, & Snyder L.E., 2002, ApJ, 576, 255.

Acknowledgements:Acknowledgements:

Dr. Brooks H. PateDr. Brooks H. Pate

Dr. Anthony Dr. Anthony RemijanRemijanDr. Robin PulliamDr. Robin PulliamDr. Edward Murphy Dr. Edward Murphy

Amanda Amanda SteberSteberDan Dan ZaleskiJustin NeillJustin Neill

Sara FitzgeraldSara FitzgeraldMatt Matt MuckleMuckle

Funding: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.

Methyl Transfer Reaction: [CH3OH2]++ HCOOH------>HC(OH+)OCH3+H2O

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.

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.

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.