Download Can Chemical Maps Indicate the Formation of Methyl Formate?

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.