Photochemical and Discharge-driven pathways to aromatics from 1,3-butadiene: Exploring aromatic production in Titan’s atmosphere. Josh J. Newby, Jaime A. Stearns, Ching-Ping Liu and Timothy S. Zwier WI06 Department of Chemistry, Purdue University West Lafayette, IN 47907

The Atmosphere of Titan From 789,000 kilometers (491,000 miles) The image scale is 4.7 kilometers (2.9 miles) per pixel. 0.7 kilometers (.43 miles) per pixel. http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1193

Titan Photochemistry Wilson, E. H., and Atreya, S. K.; Planetary and Space Science 51, 1017-1033 (2003). J. A. Miller; S. J. Klippenstein,; J. Phys. Chem. A, 105, 7254-7266, (2001).

Rxn quenched by expansion on ms timescales Photochemistry Setup Pulsed Valve Reaction Channel Rxn quenched by expansion on ms timescales 10-5 torr 355 nm UV Probe VUV Cell Excite Probe 60-200 s Excitation To diffusion pump

Jet-Cooled Spectroscopy Cools gas phase molecules to effective temperatures of a few degrees Kelvin UV-chromophore B UV C A D B C A C E B B A B A A C D C B E B* B* B C B* A A C B* Boltzmann distribution of the vibrational population prior to expansion Jet-cooled UV spectrum Collisional cooling to zero-point vibrational level Working in the gas phase allows us to remove external perturbation due to solvent effects. Supersonic expansion, shown here, provides conformation specificity and mode-selectivity by collisionally cooling the Boltzmann populations into their respective zero-point level. We use a resistively heated General Series 9 Pulsed Valve with a stagnation pressure of (1-2 bar) 90 to 100 PSI with Helium as the carrier gas in these experiments. Each of the systems that I will be presenting contain an indole UV-chromophore, which is the active UV-chromophore in the amino acid Tryptophan. By electronically exciting the cold molecules to the first excited state, then collecting the fluorescence with a PMT, we can collect an Laser induced fluorescence spectrum as shown in the figure.

Time-of-Flight Mass Spectrometer 2 stage ion acceleration pulsed valve laser port diffusion pump cryocooler Einzel lens mass gate pulser ground plate MCP Electrodes Reaction channel Insulator

Ionization Schemes VUV UVMPI R2PI VUV UVMPI Ion R2PI S1 S1 S1 S0 S0 S0 Vacuum Ultraviolet (118nm) Single photon ionization Mass Spectra B UV C A D C A C E B A B B B A A C D C B E B* B* B C A B* A C B* UVMPI Ultraviolet multiphoton ionization 2 x 266 nm (9.3 eV) Mass Spectra VUV UVMPI Ion R2PI R2PI Resonant 2 photon ionization Aromatics UV spectra of molecule S1 S1 S1 S0 S0 S0

Photochemistry Mass Spectra *Mass Gate Pulser over m/z 54*

Primary Photoproducts C3H3 CH3 C4H4 C4H5

Sensitive to aromatics Photoproducts of butadiene I C3H3 A CH3 C4H4 C4H5 VUV B III X2 C5H8 C6H6 C7H7 C7H8 C8H10 C9H8 VUV C7H7 C7H8 C8H10 C9H8 C6H6 C UVMPI (266 nm) Sensitive to aromatics

Secondary Product Onset Tertiary Product Onset Reaction Channel Kinetics Primary Product Onset Secondary Product Onset Tertiary Product Onset

MS to UV Spectrum R2PI S1 S0

Secondary Photoproducts Analysis <1 % C6H6 is benzene <1 % C7H8 is toluene C8H10 ethylbenzene C9H8 3-phenylpropyne C6H6 C9H8 C8H10 C7H7 C5H8 C7H8

Miller-Urey Experiments C4H6 C4H6 Reaction Quenched by Expansion

Reaction Quenched by Expansion Discharge C4H6 C4H6 Reaction Quenched by Expansion C9H8 C12H10 C6H6 C4H6

Discharge Products VUV Assigned by R2PI UVMPI I CH3 Ne* C3H3 C3H4/Ar* L M M II C6 C7 C8 C9 C10 C11 C12 UVMPI M S S S S S S S S M M

R2PI spectrum obtained from butadiene discharge. a.) Styrene b.) b-methylstyrene c.) indene and d.) naphthalene.

R2PI spectrum obtained from butadiene discharge. a.) Benzene b.) phenylacetylene c.) toluene and d.) indane

Interesting Spectra m/z 142 m/z 144

m/z Molecular Formula Identity Origin (cm-1) Literature (cm-1) 78 C6H6 Benzene 38616 38609* 91 C7H7 benzyl radical 22003 22000 92 C7H8 Toluene 37486 37477 102 C8H6 Phenylacetylene 36379 36369* 104 C8H8 Styrene 34769 34760 106 C8H10 o-xylene 37317 37313 m-xylene 36957 36956 p-xylene 36739 36732 Ethylbenzene 37596 37588 116 C9H8 Indene 34736 34730 118 C9H10 b-methylstyrene 34592 34586 indane 36912 36914 128 C10H8 Naphthalene 32464 32455* 142 C11H10 ??? 31738 N/A 31687 144 C11H12 34646

What is m/z 142? Benzene discharge UVMPI Butadiene discharge II C6 C7 C8 C9 C10 C11 C12 Benzene discharge UVMPI Personal Communication T. Scmidt 2006 Butadiene discharge Vinylacetylene discharge

Identification of Phenylcyclopentadienes Discharge b) Synthetic

Conformational Selectivity UV Holeburning Spectroscopy UVHB S1 S0 Hole-burn Probe B* C E B A D 50-500 nsec UV probe UV Holeburning Spectroscopy Records the UV spectrum of a single conformation free from interference from others present in the expansion UV Hole-burn laser fixed: Provides l selectivity UV probe laser tuned

Holeburning of phenylcyclopentadiene R2PI B * * A

Identification of phenylcyclopentene Discharge b) Commercial

Phenylcyclopentenes FD02

Processing by Discharge hn X discharge C4H6 C4H6 C4H6 C4D6 2 C3H3 C3H3 + C3D3 2 C3D3 C6H6 C6H3D3 C6D6

C4H6/C4D6 Discharge

Benzene 610 Bands

Statistical Benzene Formation C6H6:C6H5D:C6H4D2:C6H3D3:C6H2D4:C6HD5:C6D6 1:6:15:20:15:6:1

Integrated Mass Spectrum 1 2 1 1 6 15 20 15 6 1 H6 D1 D2 D3 D4 D5 D6

Conclusions/Future Work Products can vary by excitation. C6H6 Discharges can create a variety of neutral products Styrene, naphthalene etc. There are molecular species that may be important to the development Titan’s atmosphere that are yet to be characterized phenylcyclopentenes Phenyl Radical photochemistry discharge Radicals Indenyl Styryl Phenyl Closing the Ring

Phenyl Radical NO+ C6H5+ C6H5NO+ (C6H5)2NO+ C12H10+

National Aeronautics and Space Administration Acknowledgements Professor Timothy S. Zwier The Zwier Group Esteban Baquero TG11 V. Alvin Shubert TG08, RA07, FD07 Tracy LeGreve TF13 Nathan Pillsbury William James TG12 Chirantha Rodrigo RA09 Josh Sebree Dr. Jaime Stearns* Dr. Talitha Selby Dr. Jasper Clarkson Dr. Ching-Ping Liu* FD01 Dr. Christian Müller RA10 U.S. Department of Energy National Aeronautics and Space Administration

The Zwier Group

Discharge Products L M S

What is m/z 142? UVMPI Benzene discharge Butadiene discharge II C6 C7 C8 C9 C10 C11 C12 UVMPI Benzene discharge Personal Communication T. Scmidt 2006 Butadiene discharge Vinylacetylene discharge