Probing the photochemical processes of Titan's atmosphere

Joshua A Sebree, Purdue University

Abstract

Isomer-specific, spectroscopic studies of several CnH m species with n = 9 & 10, m = 8-12 have been carried out. Focus has been placed on species relevant to the formation or subsequent reactions of naphthalene and other fused ring systems in gasphase environments such as Titan’s atmosphere and in interstellar dust clouds. Massresolved, resonant two-photon ionization (R2PI) was used to record the jet-cooled, vibronic spectra of specific CnH m species. Double-resonant holeburning techniques were used as a means to collect structural isomer and conformer specific spectra. The ultraviolet spectrum of a new C10H8 isomer, 1-phenyl-1-butyn-3-ene, has been recorded and compared with other C10H8 isomers. Working off the hypothesis that alkylated benzenes may undergo ring closure to give fused ring species, conformationspecific spectroscopy of two radical recombination products, 4-phenyl-1-butene (C10H12) and benzylallene (C10H10), have been recorded, the former being the product of benzyl and allyl radicals, the latter of benzyl and propargyl radicals. It was found that upon photo-excitation, benzylallene undergoes hydrogen loss and ring closure to form naphthalene. It has been postulated that resonance-stabilized radicals (RSRs) play an important role in the formation of fused ring systems, including the aforementioned benzylallene to naphthalene mechanism. To that end, the visible spectroscopy and ionization thresholds of 1-phenylallyl (C9H9) and benzylallenyl (C10 H9) were recorded. The isomer-specific spectra and properties of three hydronaphthyl radicals, 1- and 2- hydronaphthyl (C10H 9), and 1,2,3-trihydronaphthyl (C10H11) have also been recorded. Hydrogenated naphthalenes may play a role in forming larger fused ring systems leading to tholins. They have also been postulated to play a role in the recycling of hydrogen in the interstellar media. Finally, the spectroscopy of two bicyclic compounds, diphenydiacetylene and diphenylvinylacetylene were explored as simple PAHs where the aromatic rings are not fused together, but are still conjugated.

Degree

Ph.D.

Advisors

Zwier, Purdue University.

Subject Area

Atmospheric Chemistry|Organic chemistry

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