novel applications of a shape-sensitive detector 3: modeling combustion chemistry through an...
TRANSCRIPT
NOVEL APPLICATIONS OF A SHAPE-SENSITIVE DETECTOR 3:
MODELING COMBUSTION CHEMISTRY THROUGH AN ELECTRIC DISCHARGE SOURCE
Giana Storck
Purdue UniversityDepartment of Chemistry
560 Oval Dr, West Lafayette, IN 47907-2084
Chandana KarunatilakaPost-Doc
Amanda ShirarGraduate Student
Kelly HotoppGraduate Student
Undergraduates: Ricky Crawley Jr., Erin Blaze Biddle
Brian C. Dian
Combustion ChemistryThe Chemistry of Combustive Materials
More efficient ways to burn fuelCleaner Chemistry throughout the combustion process (soot formation)
CharacterizationQuantitative (Rate Constants) and Qualitative (Product Identification)
Common Methods for Studying Combustion Chemistry
Fluorescence Based
Very Sensitive
Appropriate chromophore necessary
Not discriminatory
Mass based
Mass Selective
Doesn’t reveal bond connectivity
Using Our Experimental SetupBased on Rotational Spectroscopy
Only need a dipole moment
Shape sensitive
Isomeric (bond connectivity) and
Conformational (molecular shape)
Quick (10,000 avg. in ~20 minutes)
With 20 μs gate, ~170,000 data channels
Shape Sensitive TechniqueRotational Constants 1/r2
A*: 11479 MHz B: 3963 MHz C: 3819 MHz
A*: 13950 MHzB: 3309 MHzC: 3046 MHz
*H. N. Volltrauer and R. H. Schwendeman, J. Chem. Phys. 54 (1971) 260
Cyclopropanecarboxaldehyde
CisTrans
μ= reduced massr=nuclear displacement from center of mass
Experimental Setup
Reaction initiated via Penning Ionization of Ar bath.
Hot products cooled in supersonic expansion
Typical Discharge Voltage +/-500 V
Discharged pulsed 100 μs (Expansion > 1ms)
Pulsed Valve Body
Discharge Housing
Electrodes
Insulator (Delrin)
Chirped Pulse FTMW Discharge Setup
18.9 GHzPDRO
12 GHz Oscilloscope
(40 Gs/s)
ArbitraryWaveformGenerator
100 MHz Quartz Oscillator
Chirped Pulse1.875-4.675 GHz
7.5-18.5GHz
Free InductionDecay
x4
20 dB
Discharge Nozzle
Discharge Pulse
Generator
Timing Control Box
200W
Sample + Ar
Experimental Timing
Sample Pulse Drift Time Acquisition
Discharge
2,3-Dihydrofuran 2,3-DHF is found in petroleum and other fuels
Unimolecular rearrangement to Cyclopropanecarboxaldehyde (CPCA) and Crotonaldehyde (CA)
Characterization of Products through rotational spectrum.
Do we identify any new species?
A: 8084B: 7785C: 4201
000-101
Ground State Spectrum of 2,3-DHF
Corvellati, R.; Esposti, A.; Lister, D.; Lopez, J.; Alonso, J.; J. Mol. Struct. 147 (1986) 255
A: 8084B: 7785C: 4201
101-000
321-322
211-212
Near Oblate TopA-type Spectrum
Valve Difference
Using Old Discharge Valve Holder
New Discharge Nozzle
Old Discharge Nozzle
Discharge Spectrum
Cyclopropane carboxaldehyde (CPCA)
Crotonaldehyde (CA)
A. Lifshitz, M. Bidani; J. Phys. Chem., 93, (1989), pp. 1139-1144.
Trans CPCACis CPCATrans CATrans AcroleinCis AcroleinPropenePropyneFormaldehyde
Products found after a gas was put through a single pulse shock tube and were analyzed using GC/MS
Results
Experimental
SPCAT
10,000 acquisitions~20 min
Trans CPCACis CPCATrans CATrans AcroleinCis AcroleinPropenePropyneFormaldehyde
Unidentified Species
SPCAT
A: 19383B: 2356C: 2316
ΔJ=3→4Big Molecule
Theoretical Reaction Surfaces
Adapted from:F. Dubnikova, A. Lifshitz, J. Phys. Chem. A; v.106 (2002) pp. 1026-1034.
Barrier ~ 20,000 cm-1
ΔE
(kca
l/mo
l)
CyclopropanecarboxaldehydeCrotonaldehyde
Transitions found using STQN method and verified using IRC at B3LYP level
ΔE
(kca
l/mo
l) Cis!
ΔE
(kca
l/mo
l)
CA vs. CPCA Torsional PotentialB3LYP/6-31+G**
*1550 cm-1 *1532 cm-1
**2034 cm-1 **1920 cm-1
2117 cm-1 2076 cm-1
E = 689 cm-1
B3LYP/6-31+G**3493 cm-1 2804 cm-1
*H. N. Volltrauer and R. H. Schwendeman, J. Chem. Phys. 54 (1971) 260
ΔE= 57 cm-1
Trans:A: 32636B: 2183C: 2073
202-101
303-202
404-303
Cis:A: 19186B: 2609C: 2330
202-101
303-202
404-303
202-101 303-202
10,000 acquisitions~20 min.
Ground State Rotational Spectrum of Crotonaldehyde
Unidentified Species
SPCAT
Unidentified Species:A: 19383B: 2356C: 2316
Cis Crotonaldehyde:A: 19186B: 2609C: 2330
Summary What did we learn?
1) It’s not Cis-Crotonaldehyde2) Near Prolate Top
-structure is something like CA3) Splitting on K1 bands suggest it has a
methyl rotor4) Biggest shift along the B-moment
Our best guess at this time is that it could be a radical species
But:-net increase in mass-no evidence for spin-rotation coupling
Argon Cluster?
Some Future WorkQuantitativeUse intensity information to get
concentrations and possibly rate information
Using different chemicals (dimolecular reactions)
Benzyne+ oxygen
Acknowledgements
Dian Group
Dr. Brian DianDr. Chandana KarunatilakaAmanda ShirarKelly HotoppRicky CrawleyErin Blaze Biddle
Funding
ACS- PRF G