Centers for Chemical Innovation July.30.2010 Arianna Seabrooks, Jasmine Mays, Jasmine Drake, Anthony Speas
Broadband Spectrometer Potential Energy Surfaces Reaction Pathways Further Work
Gordon G. Brown, Brian C. Dian, Kevin O. Douglass, Scott M. Geyer, Steven T. Shipman, and Brooks H. Pate, Rev. Sci. Instrum. 79, 053103, (2008).
http://www.thomasnet.com/articles/automation-electronics/electronic-microwave-manufacturing
a Axis c Axis b Axis I m r i i 2 i A 1 I, B 1 I 1, C A I C B Rotational constants and moments of inertia are governed by the shape of the molecule In order to see a rotational spectrum, a dipole moment is required http://smoknjoe.tripod.com/aviation.htm
Study unique species These unique species consist of ions, radicals, and high energy isomers All three can be found in the interstellar medium The discharge can reproduce the interstellar species Main focus : High Energy Isomers
Discharge is used to identify the weaker lines in the spectra. Provides energy in. Up to 2 kv discharge can be applied. Jens-Uwe Grabow, E. Samuel Palmer, Michael C. McCarthy, and Patrick Thaddeus, Rev. Sci. Instrum. 76, 093106, (2005).
Experimental Settings 10 psi backing pressure 0.2% methyl formate/neon carrier gas Expanded through a 1mm General Valve series 9 nozzle 300K averages
Ab Initio Calculations: optimization Energetics Rotational Constants Structures
Potential energy surfaces are the energy of the molecule as a function of its structure As the structure is changed, the energy changes The relative accuracy of the energies is based on the level of theory used to calculate them. 1 2 Cis
Trans Potential Energy Scan maps out the flow of energy as the structure of the molecule is changing Cis
kt(100k) ~ 70 cm -1 << 5000 cm -1 barrier Trans is about 2000 cm -1 higher in energy 5000 cm -1 isomerization barrier At 100K virtually no isomerization occurs Equilibrium cis/trans ratio ~10 12 : 1 at 100K ~14000:1 at 300K The amount of trans methyl formate detected in space suggests kinetic control cis: µ a = 1.7 D µ b = 1.1 D trans: µ a = 4.3 D µ b = 2.5 D Calculations done at the MP2 6-31G++(d,p) level of theory
Intensity (mv) Intensity (mv) Frequency (MHz) Frequency (MHz)
Reactive Chemistry Fischer Esterification Methyl Transfer
Favors production of cis methyl formate Needs energy input within the system to react Has a higher activation energy barrier than that of the methyl transfer reaction Possibly occurs near star forming areas Begins with a protonated Formic acid molecule
Energy (kj/mol) CH 3 OH + [HCO(OH) 2 ] + [HC(OH)OCH 3 ] + + H 2 O E a sym = +17.4 kj/mol E a anti = +21.2 kj/mol
Reaction pathway predicts the formation of trans-methyl formate Differs from Fischer Esterification method by the reactants (Methanol is Protonated in methyl transfer pathway)
Energy (kj/mol) off off [CH 3 OH 2 ] + + HCOOH [HC(OH)OCH 3 ] + + H 2 O E a sym = 13.3 kj/mol E a anti = -5.3 kj/mol
Lactic Acid Ethyl Formate Acetonitrile + H 2 O Allene + CO 2
As a way to study biological systems ; structure affects function See how water attaches to lactic acid molecules in a system because if it is possible to see how other molecules attach to water than it would be possible to understand how it is done in the body Chiral molecule which means its mirror image is non super imposable Pszczółkowski a, Białkowska-Jaworska a, Kisiel, J. Mol. Spec. 234, 106-112, (2005). Van Eijck. J. Mol. Spec., 101, 133-138, (1983).
Experimental Settings 30 psi backing pressure Lactic acid in reservoir nozzles (90/10 with water) Neon carrier gas Heated to 90 o C
Experimental Rotational Constants (MHz) Computational Rotational Constants Structure I (MHz) Computational Rotational Constants Structure II (MHz) 4965.987 (48) 1336.9117 (12) 1127.4466 (10) 4480.76 3001.49 1362. 39 1912.05 1149.89 1477.58 *Four distortion parameters also fitted but not shown. 6-311 ++ G (d, p)/m05-2x Smaga, Sadlej. J. Phys. Chem. A, 114, 4427-4436, (2010).
polar RS
RR Non-polar
Broadband aids in the identification of unique species There are two conformers of methyl formate Cis Trans Fischer Esterification favors cis methyl formate; Methyl Transfer favors trans methyl formate Trans has been located in the interstellar medium The abundance of trans suggest a more kinetic control vs. thermodynamic (heat). To date, an unsaturated water spectrum of lactic acid has not been taken. We have assigned lactic acid monomer and one water and are currently looking for larger clusters.
Amanda Steber, Daniel Zaleski, Justin Neill, Matt Muckle, Brooks Pate University of Virginia Anthony Remijan National Radio Astronomy Observatory Valerio Lattanzi, Silvia Spezzano, Michael McCarthy Harvard-Smithsonian Center for Astrophysics Zbigniew Kisiel Institute of Physics, Polish Academy of Sciences Rick Suenram National Institute of Standards and Technology Centers for Chemical Innovation Award Number 0847919