Size effects on dissociation rates of polycyclic aromatic hydrocarbon cations: Laboratory studies and astophysical implications

Jochims, H.‐W.; Rühl, E.; Baumgärtel, H.; Tobita, Seiji; Leach, Sydney

doi:10.1086/173560

Cited by 209 publications

(271 citation statements)

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“…This leads to a probability lower than 0.01 only for PAHs with N C > ∼ 30, which is in accordance with previous estimates (Jochims et al 1994). We now consider electron collisional heating.…”

Section: Pah Dissociation Probabilitysupporting

confidence: 91%

“…where P(n max ) is the total un-normalized dissociation probability after the ejection of n max photons, the average temperature, E av , is chosen as the geometric mean (E av = E tr × E n max ), E n max = (E tr −n max ×Δ ) and k IR is assumed to be 100 photons s −1 (Jochims et al 1994). We apply this method to put a lower limit on the dust population sizes for both photon and electron collisional heating.…”

Section: Pah Dissociation Probabilitymentioning

confidence: 99%

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Dust heating

Bocchio

Jones

Verstraete

et al. 2013

A&A

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Aims. We investigate and quantify the effects of the electron collisional heating of dust in a hot gas and compare this with photon heating by the interstellar radiation field. Methods. We compare the rate of energy absorption by dust due to electron collisional and photon heating as a function of the physical conditions of the gas and the ambient radiation field. We calculate the resulting dust spectral energy distributions (SEDs) for different environments.Results. We find that electron collisions and grain charging effects in a hot gas (10 6 −10 7 K) rapidly destroy small carbonaceous particles and result in a minimum particle size of the order of a few nm. The charging due to the emission of secondary electrons is important and leads to high electric potentials, which quickly destroy the small grains by field ion emission. In the case of weak interstellar radiation fields (G 0 ∼ 0.1), electron collisional heating can be the dominant heating process and therefore makes an important contribution to the dust thermal emission. Conclusions. Collisions of electrons with dust grains, in a hot gas, lead to important changes in the dust SED, as a result of their high energy input. We find that grain charge effects and accompanying erosion need to be taken into account in the calculation of the dust SED. The power absorbed by the dust as a result of electron collisions in a hot tenuous gas can be larger than that due to photon absorption in the intergalactic medium close to a galaxy where the radiation field is weak (G 0 < ∼ 0.1).

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Section: Pah Dissociation Probabilitysupporting

confidence: 91%

Section: Pah Dissociation Probabilitymentioning

confidence: 99%

Dust heating

Bocchio

Jones

Verstraete

et al. 2013

A&A

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“…Jochims et al (1994) showed that small PAHs (N C 30−40) will dissociate, before they can relax by IR emission, in HI regions and will therefore be rapidly destroyed in the low-density, diffuse ISM. Thus, the fragmentation products of sub-nm, a-C(:H) particles, i.e., aromatic clusters with few aromatic rings (N R = 2−3) and only 10-20 sp 2 carbon atoms, are likely to be rather short-lived in the ISM.…”

Section: Structural Variations and Spectral Propertiesmentioning

confidence: 99%

Variations on a theme – the evolution of hydrocarbon solids

Jones

2012

A&A

102

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Context. The properties of hydrogenated amorphous carbon (a-C:H) dust evolve in response to the local radiation field in the interstellar medium (ISM) and the evolution of these properties is particularly dependent upon the particle size. Aims. A model for finite-sized, low-temperature amorphous hydrocarbon particles, based on the microphysical properties of random and defected networks of carbon and hydrogen atoms, with surfaces passivated by hydrogen atoms, has been developed. Methods. The eRCN/DG and the optEC (s) models have been combined, adapted and extended into a new optEC (s) (a) model that is used to calculate the optical properties of hydrocarbon grain materials down into the sub-nanometre size regime, where the particles contain only a few tens of carbon atoms. Results. The optEC (s) (a) model predicts a continuity in properties from large to small (sub-nm) carbonaceous grains. Tabulated data of the size-dependent optical constants (from EUV to cm wavelengths) for a-C:H (nano-)particles as a function of the bulk material band gap [E g (bulk)], or equivalently the hydrogen content, are provided. The effective band gap [E g (eff.)] is found to be significantly larger than E g (bulk) for hydrogen-poor a-C(:H) nano-particles and their predicted long-wavelength (λ > 30 μm) optical properties differ from those derived for interstellar polycyclic aromatic hydrocarbons (PAHs). Conclusions. The optEC (s) (a) model is used to investigate the size-dependent structural and spectral evolution of a-C(:H) materials under ISM conditions, including: the IR-FUV extinction, the 217 nm bump and the infrared emission bands. The model makes several predictions that can be tested against observations.

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“…Useli-Bacchitta et al (2010) noted that loss of C 2 H 2 is seen when excitation of the methyl-substituted pyrene cation takes place with photons in the visible spectral range. This channel has also been observed for non methyl-substituted PAHs when colliding with ions (Holm et al 2010) and 7-35 eV photons (Gotkis et al 1993;Jochims et al 1994). To clarify which pathway is actually observed, transition-state calculations have been carried out for the loss of C 2 H 3 and the lowest barrier is It is clearly seen that the dissociation time spans over several milliseconds.…”

Section: Fragmentation Channelsmentioning

confidence: 71%

UV action spectroscopy of protonated PAH derivatives

Klærke

Holm

Andersen

2011

A&A

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Aims. We investigate the production of molecular photofragments upon UV excitation of PAH derivatives, relevant for the interstellar medium. Methods. The action absorption spectra of protonated gas-phase methyl-substituted quinolines (CH 3 −C 9 H 7 NH + ) have been recorded in the 215-338 nm spectral range using the electrostatic storage ring ELISA, an electrospray ion source and 3 ns UV laser pulses. Results. It is shown that the absorption profile is both redshifted and broadened when moving the methyl group from the heterocycle containing nitrogen to the homoatomic ring. The absorption profiles are explained by TD-DFT calculations. The dissociation time of the studied molecules is found to be of several milliseconds at 230 nm and it is shown that after redistribution of the absorbed energy the molecules dissociate in several channels. The dissociation time found is an order of magnitude faster than the estimated IR relaxation time. Photophysical properties of both nitrogen containing and methyl-substituted PAHs are interesting in an astrophysical context in connection with identifying the aromatic component of the interstellar medium.

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Size effects on dissociation rates of polycyclic aromatic hydrocarbon cations: Laboratory studies and astophysical implications

Cited by 209 publications

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Dust heating

Dust heating

Variations on a theme – the evolution of hydrocarbon solids

UV action spectroscopy of protonated PAH derivatives

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