Isomer specific spectroscopy of C10Hn, n = 8-12: exploring pathways to naphthalene in Titan's atmosphere

Faraday Discuss. 2010;147:231-49; discussion 251-82. doi: 10.1039/c003657a.

Abstract

Laboratory investigations of the isomer-specific spectroscopy of several C10Hn isomers with n = 8-12 are described, focusing on structures of relevance to the formation or subsequent reaction of naphthalene. The photochemical models of Titan's atmosphere have now progressed to the point that further development of the large-molecule end of the model must recognize and explicitly incorporate the unique spectroscopy, photochemistry, and reactivity of structural isomers. Mass-resolved, resonant two-photon ionization (R2PI) was used to record ultraviolet spectra of specific C10Hn composition, while hole-burning methods were used to resolve the spectra of different structural and conformational isomers under jet-cooled conditions. The R2PI spectrum of a new C10H8 isomer, 1-phenyl-1-butyne-3-ene, is described and contrasted with other C10H8 isomers. The anticipated role for resonance-stabilized radicals is illustrated by studies of the visible spectroscopy of two hydronaphthyl radical isomers, 1-C10H9 and 2-C10H9, and the trihydronaphthyl radical 1,2,3-C10H11. Conformation-specific spectra of an anticipated C10H12 recombination product of benzyl and allyl radicals is also reported. A reaction scheme that fleshes out the experimental data surrounding naphthalene and its hydrogenated radicals and ions is proposed as a basis for future modeling under Titan's conditions.