C and N fractionation of CH/N mixtures during photochemical aerosol formation: Relevance to Titan.

The ratios of the stable isotopes that comprise each chemical species in Titan's atmosphere provide critical information towards understanding the processes taking place within its modern and ancient atmosphere. Several stable isotope pairs, including C/C and N/N, have been measured or probed spectroscopically by Cassini-borne instruments, space telescopes, or through ground-based observations. Current attempts to model the observed isotope ratios incorporate fractionation resulting from atmospheric diffusion, hydrodynamic escape, and primary photochemical processes.

Photochemistry of benzylallene: ring-closing reactions to form naphthalene.

Conformer-specific, vibrationally resolved electronic spectroscopy of benzylallene (4-phenyl-1,2-butadiene) is presented along with a detailed analysis of the products formed via its ultraviolet photoexcitation. Benzylallene is the minor product of the recombination of benzyl and propargyl radicals. The mass-selective resonant two-photon ionization spectrum of benzylallene was recorded under jet-cooled conditions, with its S(0)-S(1) origin at 37,483 cm(-1).

The excited states and vibronic spectroscopy of diphenyldiacetylene and diphenylvinylacetylene.

Laser induced fluorescence (LIF) excitation scans and dispersed fluorescence (DFL) spectra have been recorded for two four-carbon α,ω-diphenyl systems, diphenyldiacetylene (DPDA, φ-C≡C-C≡C-φ) and trans-diphenylvinylacetylene (DPVA, φ-CH≡CH-C≡C-φ) as isolated molecules cooled in a supersonic expansion. While these molecules have similar conjugation length, they exhibit strikingly different vibronic spectroscopy and photophysics. The near-UV LIF excitation spectrum of diphenyldiacetylene has its electronic origin at 32,158 cm(-1), and a strong progression in the C≡C stretch (2156 cm(-1)).

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

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.

Spectroscopic and thermochemical consequences of site-specific H-atom addition to naphthalene.

Vibronic spectra of doublet-doublet transitions of 1-hydronaphthyl (1HN), 2-hydronaphthyl (2HN), and 1,2,3-trihydronaphthyl (THN, tetralyl) radicals have been recorded under jet-cooled conditions. Transitions due to the two C(10)H(9) isomers were identified and assigned based on the choice of radical precursor, visible-visible hole-burning spectroscopy, comparison of observed vibronic transitions with calculation, and photoionization efficiency scans. The latter provided accurate ionization potentials for the three free radicals (IP(1HN) = 6.

Structure and dynamics of phthalocyanine-argonn (n = 1-4) complexes studied in helium nanodroplets.

Van der Waals clusters of phthalocyanine with 1-4 argon atoms formed inside superfluid helium nanodroplets have been investigated by recording fluorescence excitation spectra as well as emission spectra. The excitation spectra feature a multitude of sharp lines when recorded in superfluid helium droplets in contrast to the respective spectra measured in a seeded supersonic beam (Cho et al. Chem.