Generalized oscillator strength for the 1B2u←1Ag transition and the observation of forbidden processes at the C 1s spectrum of the naphthalene molecule

Souza, G. G. B. de; Boechat-Roberty, H. M.; Rocco, Maria Luiza M.; Lucas, C.A.

doi:10.1016/s0368-2048(02)00038-5

Cited by 7 publications

(3 citation statements)

References 36 publications

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“…The photon absorption cross section of PAHs shows strong peaks at about 6 and 17.5 eV associated with transitions involving the π and σ electronic manifolds and then another broad peak around 286 eV due to carbon K-shell transitions (Keller et al 1992;de Souza et al 2002;Regier et al 2007). Each of these peaks can show various subpeaks due to electronic and vibrational structure.…”

Section: X-ray Absorptionmentioning

confidence: 99%

Polycyclic aromatic hydrocarbon processing in a hot gas

Micelotta

Jones

Tielens

2010

A&A

164

180

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Context. PAHs are thought to be a ubiquitous and important dust component of the interstellar medium. However, the effects of their immersion in a hot (post-shock) gas have never before been fully investigated. Aims. We study the effects of energetic ion and electron collisions on PAHs in the hot post-shock gas behind interstellar shock waves. Methods. We calculate the ion-PAH and electron-PAH nuclear and electronic interactions, above the carbon atom loss threshold, in H ii regions and in the hot post-shock gas for temperatures ranging from 10 3 −10 8 K. Results. PAH destruction is dominated by He collisions at low temperatures (T < 3 × 10 4 K), and by electron collisions at higher temperatures. Smaller PAHs are destroyed faster for T < 10 6 K, but the destruction rates are roughly the same for all PAHs at higher temperatures. The PAH lifetime in a tenuous hot gas (n H ≈ 0.01 cm −3 , T ≈ 10 7 K), typical of the coronal gas in galactic outflows, is found to be about thousand years, orders of magnitude shorter than the typical lifetime of such objects. Conclusions. In a hot gas, PAHs are principally destroyed by electron collisions and not by the absorption of X-ray photons from the hot gas. The resulting erosion of PAHs occurs via C 2 loss from the periphery of the molecule, thus preserving the aromatic structure. The observation of PAH emission from a million degree, or more, gas is only possible if the emitting PAHs are ablated from dense, entrained clumps that have not yet been exposed to the full effect of the hot gas.

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Section: X-ray Absorptionmentioning

confidence: 99%

Polycyclic aromatic hydrocarbon processing in a hot gas

Micelotta

Jones

Tielens

2010

A&A

164

180

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“…The absolute GOS results are presented in figure 3 and in table 1 as a function of K 2 . Extrapolation using the universal curve has been previously used in our laboratory, in electron impact studies of the anthracene, naphthalene and benzene molecules (Boechat-Roberty et al 1997, 2004, de Souza et al 2002. A theoretical analysis, based on the use of a universal extrapolation formula for the GOS (Fomunung et al 1996), has also shown, for example, that our experimental values extrapolate nicely to the optical oscillator strength for the C 1s transition in the CO 2 molecule (Boechat-Roberty et al 1991).…”

Section: Inelastic Differential θ (Degrees)mentioning

confidence: 71%

Cross sections for elastic and inelastic electron scattering from carbon disulfide

Boechat-Roberty

Ferreira-Rodrigues

Turci

et al. 2006

J. Phys. B: At. Mol. Opt. Phys.

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Electron energy-loss spectra, measured as a function of the scattering angle, have been obtained for a carbon disulfide molecule, CS2, in the excitation energy range from 0 to 45 eV. The incident electron energy was 1000 eV. The absolute generalized oscillator strength (GOS) and absolute inelastic differential cross section have been determined as a function of the square of the momentum transfer (K2) for the intense allowed transition 1Σ+u ← 1Σ+g, centred at 6.3 eV. The absolute elastic differential cross section was also determined spanning an angular range from 1.5° to 10°. It is well known that at high incident energies and small scattering angles electrons behave like pseudo photons. The CS2 photoabsorption spectrum was consequently obtained by extrapolation from the measured small angle electron energy-loss spectrum. The result shows a good resemblance to the atmospheric spectrum of Jupiter, following comet impact.

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“…We have obtained photoabsorption spectra converted from the electron energy-loss spectra for molecules such as benzene, naphthalene and anthracene (Boechat-Roberty 679 et al 2004, de Souza et al 2002, Boechat-Roberty et al 1997) and other species. Briefly, we have measured electron energy-loss spectra (EELS) at electron incident energy of 1000 eV and small scattering angles.…”

Section: Methodsmentioning

confidence: 99%

Photoabsorption of hydrocarbons in Titan's atmosphere

2009

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Abstract. Titan, the largest satellite of the planet Saturn, has a thick atmosphere which consists of nitrogen (N2 ) and methane (CH4 ). In 2004, the Cassini-Huygens mission observed the occultation of two stars through the atmosphere of Titan and measured ultraviolet (UV) absorption spectra. Through these spectra it was possible to identify the molecular species contained in this environment. In the present work, we have simulated a spectrum of this atmosphere using some molecules such as CH 4 , C2 H2 , C2 H4 , C2 H6 , C4 H2 , and C6 H6 . Our cross sections data were experimentally obtained using the electron energy-loss technique, where the electron energy-loss spectra, measured high incident energies and in small scattering angles, are similar to photoabsorption spectra. The comparison of our synthetic spectrum with that measured by Cassini shows that this method is very efficient for identifying molecules as well as estimating abundances.

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Generalized oscillator strength for the 1B2u←1Ag transition and the observation of forbidden processes at the C 1s spectrum of the naphthalene molecule

Cited by 7 publications

References 36 publications

Polycyclic aromatic hydrocarbon processing in a hot gas

Polycyclic aromatic hydrocarbon processing in a hot gas

Cross sections for elastic and inelastic electron scattering from carbon disulfide

Photoabsorption of hydrocarbons in Titan's atmosphere

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