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