Photoionization measurement of the triplet lifetime of benzene

Duncan, M. A.; Dietz, T. G.; Liverman, M. G.; Smalley, R. E.

doi:10.1021/j150601a003

Cited by 104 publications

(53 citation statements)

References 2 publications

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“…This is the decay rate that represents the metastable lifetime for an isolated molecule, and one that we can measure by using a UV-pump, VUV-probe strategy. In this approach, analogous to early studies by Smalley and coworkers (25,26), the nanosecond UV laser excites C 4 H 2 , after which it relaxes rapidly to T 1 . A 7.9-eV (157 nm, F 2 excimer) probe laser can then ionize the electronically excited states of (27)], but not the ground state.…”

Section: Resultsmentioning

confidence: 91%

H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

Silva

Gichuhi

Huang

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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We present an experimental investigation of the UV photochemistry of diacetylene under collisionless conditions. The H loss channel is studied using DC slice ion imaging with two-color reduced-Doppler detection at 243 nm and 212 nm. The photochemistry is further studied deep in the vacuum UV, that is, at Lymanalpha (121.6 nm). Translational energy distributions for the H ؉ C 4H product arising from dissociation of C 4H2 after excitation at 243, 212, and 121.6 nm show an isotropic angular distribution and characteristic translational energy profile suggesting statistical dissociation from the ground state or possibly from a low-lying triplet state. From these distributions, a two-photon dissociation process is inferred at 243 nm and 212 nm, whereas at 121.6 nm, a one-photon dissociation process prevails. The results are interpreted with the aid of ab initio calculations on the reaction pathways and statistical calculations of the dissociation rates and product branching. In a second series of experiments, nanosecond time-resolved phototionization measurements yield a direct determination of the lifetime of metastable triplet diacetylene under collisionless conditions, as well as its dependence on excitation energy. The observed submicrosecond lifetimes suggest that reactions of metastable diacetylene are likely to be less important in Titan's atmosphere than previously believed.ion imaging ͉ photochemistry ͉ Titan S aturn's moon, Titan, is the only solar system body besides Earth and Venus with a dense atmosphere (1, 2). It is widely considered as a natural laboratory on the planetary scale in understanding the prebiotic chemistry on proto-Earth. Diacetylene is believed to play a key role in the formation of polyynes and polycyclic aromatic hydrocarbons (PAHs) that partially comprise the haze layer in Titan's upper atmosphere (2-4). It is well established that the formation of diacetylene is initiated by photodissociation of acetylene below 217 nm (2, 5-8) according to the following reaction mechanism:The importance ascribed to diacetylene arises in part because it absorbs light at longer wavelengths, where the solar flux is higher, than any other major constituents of Titan's atmosphere; moreover, experimental results suggest it is still photochemically reactive even well below the threshold for dissociation (9-12). Understanding the dynamics of diacetylene photoexcitation is thus key to revealing the factors driving the chemistry of Titan's atmosphere.To date, no experiments on the photochemistry of diacetylene have been performed under collisionless conditions. In a pioneering study, Glicker and Okabe (9) determined a quantum yield of 2.0 Ϯ 0.5 for diacetylene photodissociation in the wavelength region of 147-254 nm. Between 184 and 254 nm, no free-radical products were detected and polymeric material was found to coat the inside of the reaction cell. The upper limit for the quantum yield of C 4 H formation was then determined to be only 0.06 at 228 nm based on experimental uncertainty. However, at the time, t...

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Section: Resultsmentioning

confidence: 91%

H elimination and metastable lifetimes in the UV photoexcitation of diacetylene

Silva

Gichuhi

Huang

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…An obvious mediator for the increased production of I+ in the high pressure expansion is the I2 molecular product. A possible source of I+ may result from the photodecomposition of I2+, formed via reactions 4 and 5 hu IZ+-+I+I+ (13) The mechanism requires five photons, more than needed for direct ionization of I*. However, excitation would involve molecular species, I2 and 12+, which have broad absorptions leading to resonance enhanced cross sections compared to the nonresonant process in I atoms.…”

Section: I+ + H I -I+ + H (3)mentioning

confidence: 99%

Photochemistry in HI Clusters via Excitation of the First UV Continuum

Young¹

1994

J. Phys. Chem.

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Photochemistry in HI cluster species, generated in a seeded supersonic expansion, was initiated by laser excitation into the first UV continuum and probed by photoionization within the same laser pulse. Only one new product species was detected, Iz+, but the HI+, H+, and I+ signals all show the effects of cluster formation. The I2 product is formed in the neutral complex through a two-photon process rather than a single-photon event. The laser intensity dependence of the HI+ and I+ signals increases due to new mechanisms of production that become active in the cluster. The HI+ wavelength spectrum is perturbed, but no ions of the type (HI)"+ are detected, possibly due to a large geometry change subsequent to ionization which results in rapid fragmentation. Our studies constitute the first detailed probes of photochemistry occurring in hydrogen halide clusters.

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“…Now it is generally recognized that nonadiabatic processes play an important role in photodissociation dynamics of benzene. [1][2][3][4] For instance, the hot-benzene mechanism has been proposed to account for the observed experimental results. 5,6 The hot benzene is highly vibrationally excited ground electronic state benzene, which is produced by internal conversion from the electronically excited singlet states populated after photoexcitation.…”

Section: Introductionmentioning

confidence: 99%