NOVEL APPLICATIONS OF A SHAPE-SENSITIVE DETECTOR 3: MODELING COMBUSTION CHEMISTRY THROUGH AN ELECTRIC DISCHARGE SOURCE Giana Storck Purdue University Department of Chemistry 560 Oval Dr, West Lafayette, IN Chandana Karunatilaka Post-Doc Amanda Shirar Graduate Student Kelly Hotopp Graduate Student Undergraduates: Ricky Crawley Jr., Erin Blaze Biddle Brian C. Dian

Combustion Chemistry  The Chemistry of Combustive Materials  More efficient ways to burn fuel  Cleaner Chemistry throughout the combustion process (soot formation)  Characterization  Quantitative (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 Setup  Based 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 Technique Rotational Constants  1/  r 2 A*: MHz B: 3963 MHz C: 3819 MHz A*: MHz B: 3309 MHz C: 3046 MHz *H. N. Volltrauer and R. H. Schwendeman, J. Chem. Phys. 54 (1971) 260 Cyclopropanecarboxaldehyde Cis Trans μ= reduced mass r=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 GHz PDRO 12 GHz Oscilloscope (40 Gs/s) Arbitrary Waveform Generator 100 MHz Quartz Oscillator Chirped Pulse GHz GHz Free Induction Decay 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: 8084 B: 7785 C: Ground State Spectrum of 2,3-DHF Corvellati, R.; Esposti, A.; Lister, D.; Lopez, J.; Alonso, J.; J. Mol. Struct. 147 (1986) 255 A: 8084 B: 7785 C: Near Oblate Top A-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 Trans CPCA Cis CPCA Trans CA Trans Acrolein Cis Acrolein Propene Propyne Formaldehyde 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 CPCA Cis CPCA Trans CA Trans Acrolein Cis Acrolein Propene Propyne Formaldehyde

Unidentified Species SPCAT A: B: 2356 C: 2316 ΔJ=3→4 Big Molecule

Theoretical Reaction Surfaces Adapted from: F. Dubnikova, A. Lifshitz, J. Phys. Chem. A; v.106 (2002) pp Barrier ~ 20,000 cm -1 ΔE(kcal/mol) Cyclopropanecarboxaldehyde Crotonaldehyde Transitions found using STQN method and verified using IRC at B3LYP level ΔE(kcal/mol) Cis! ΔE(kcal/mol)

CA vs. CPCA Torsional Potential B3LYP/6-31+G** * 1550 cm -1* 1532 cm -1 ** 2034 cm -1** 1920 cm cm cm -1  E = 689 cm -1 B3LYP/6-31+G** 3493 cm cm -1 *H. N. Volltrauer and R. H. Schwendeman, J. Chem. Phys. 54 (1971) 260 ΔE= 57 cm -1

Trans: A: B: 2183 C: Cis: A: B: 2609 C: ,000 acquisitions ~20 min. Ground State Rotational Spectrum of Crotonaldehyde

Unidentified Species SPCAT Unidentified Species: A: B: 2356 C: 2316 Cis Crotonaldehyde: A: B: 2609 C: 2330

Summary What did we learn? 1) It’s not Cis-Crotonaldehyde 2) Near Prolate Top -structure is something like CA 3) Splitting on K1 bands suggest it has a methyl rotor 4) 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 Work  Quantitative  Use intensity information to get concentrations and possibly rate information  Using different chemicals (dimolecular reactions)  Benzyne  + oxygen

Acknowledgements Dian Group Dr. Brian Dian Dr. Chandana Karunatilaka Amanda Shirar Kelly Hotopp Ricky Crawley Erin Blaze Biddle Funding ACS- PRF G