UV photodestruction of CH bonds and the evolution of the 3.4 $\mathsf{\mu}$m feature carrier

Mennella, V.; Muñoz, G. M.; Ruiterkamp, R.; Schütte, W. A.; Greenberg, J. Mayo; Brucato, J. R.; Colangeli, L.

doi:10.1051/0004-6361:20000340

Cited by 101 publications

(87 citation statements)

References 31 publications

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“…Muñoz-Caro and collaborators have simulated analogs of carbonaceous dust grains in dense and diffuse interstellar medium. Mennella et al (2001) have found that the irradiated hydrogenated carbon grains coated with H 2 O or H 2 O+CO+NH 3 ice layer (as an analog of dust in the dense interstellar medium) have higher reduction than those coated with the Ar ice layer (as an analog of dust in the diffuse interstellar medium). On the other hand, for a similar analog for dust in the dense and diffuse interstellar medium, Muñoz-Caro et al (2001) have found that hexane samples covered with H 2 O ice layer have lower reduction than those covered with the Ar ice layer.…”

Section: The 3-8 μM Spectral Rangementioning

confidence: 99%

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Gadallah

Mutschke

Jäger

2012

A&A

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Context. Mid-infrared (MIR) bands are characteristic for the short-range and medium-range structure of hydrogenated amorphous carbon (HAC) materials that exist in the interstellar medium (ISM) and are sensitive to processing in the harsh interstellar radiation field. Aims. We study the variability of the MIR features from the spectrum of non-processed to that of UV-processed HAC materials and compare them to spectra of interstellar carbonaceous materials. Methods. Nano-sized HAC materials produced by laser ablation were irradiated by vacuum-UV photons with doses comparable to those relevant for interstellar processing. They were subsequently analyzed by IR spectroscopy. Results. In the MIR range, the spectra of HAC materials show many absorption bands such as the sp 3 aliphatic ≡C-H stretching vibration at 3.03 μm, the sp 3 aliphatic -C-H stretching vibration at 3.4 μm and also the sp 3 aliphatic C-H bending vibration at both 6.85 μm and 7.25 μm. All these are recognizable bands of HAC materials. Other absorption bands such as the sp 2 aromatic =C-H stretching vibration at about 3.3 μm and the sp 2 -C=C stretching vibration close to 6.25 μm are observed. The HAC materials also possess bands which represent the aromatic out-of-plane bending at 11.65, 12.46 and 12.9 μm in addition to the aromatic -C-C-C in-plane bending at 15.87 μm. With UV irradiation, the mass absorption coefficient of the 3.03 μm band completely disappears and that of the aliphatic C-H bands (3.4, 6.85 and 7.25 μm) decreases. This reduction shows that the UV radiation destroys most of the aliphatic C-H bonds inside the HAC structure. On the other hand, the strength of the aromatic 6.2 μm band increases, which is evidence of the partial graphitization within UV-irradiated HAC materials. Because UV irradiation is not uniform, this band agrees well with the C-class PAH toward HD 100764. The C-H out-of-plane vibration bands are strongly affected by UV irradiation. Bands at 11.35, 12.14 and 12.64 μm (solo, duo and trio, respectively), which are found for PAHs of many interstellar spectra were observed partially and were compared to those of non-processed materials, in particular, those at 11.35 μm, which represent the aromatic structures. Conclusions. UV irradiation has a variable effect on both aliphatic and aromatic bands in the MIR region. The aliphatic C-H structure decreases while the aromatic C=C structure, which might lead to the graphitic colonies for PAHs, increases. UV irradiation has revealed solo, duo and trio bands that are relatively consistent with those of the A-and B-class PAHs.

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Section: The 3-8 μM Spectral Rangementioning

confidence: 99%

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Gadallah

Mutschke

Jäger

2012

A&A

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“…The C 2 H 2 and HCN spectra are also calculated using the HITRAN database (Rothman et al 1998) and shown in the bottom of the panel. et al (1995) but in the diffuse ISM where the destruction of C-H bonds by UV photolysis is equilibrated by rehydrogenation with ample atomic hydrogen (Mennella et al 2001(Mennella et al , 2002. Tielens et al (1994) proposed a similar mechanism for the formation of aliphatic C-H bonds by hydrogenation of a graphite surface amorphized by the ion bombardment in the interstellar shocks.…”

Section: Variations Of Aliphatic and Aromatic Abundancementioning

confidence: 99%

Spatially Resolved 3 Micron Spectroscopy of IRAS 22272+5435: Formation and Evolution of Aliphatic Hydrocarbon Dust in Proto–Planetary Nebulae

Goto

Gäessler

Hayano

et al. 2003

ApJ

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We present medium-resolution 3 lm spectroscopy of the carbon-rich proto-planetary nebula IRAS 22272+5435. Spectroscopy with the Subaru Telescope adaptive optics system revealed a spatial variation of hydrocarbon molecules and dust surrounding the star. The rovibrational bands of acetylene (C 2 H 2 ) and hydrogen cyanide (HCN) at 3.0 lm are evident in the central star spectra. The molecules are concentrated in the compact region near the center. The 3.3 and 3.4 lm emission of aromatic and aliphatic hydrocarbons is detected at 600-1300 AU from the central star. The separation of spatial distribution between gas and dust suggests that the small hydrocarbon molecules are indeed the source of solid material and that the gas left over from the grain formation is being observed near the central star. The intensity of aliphatic hydrocarbon emission relative to the aromatic hydrocarbon emission decreases with distance from the central star. The spectral variation is well matched to that of a laboratory analog thermally annealed with different temperatures. We suggest that either the thermal process after the formation of a grain or the variation in the temperature in the dust-forming region over time determines the chemical composition of the hydrocarbon dust around the proto-planetary nebula.

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“…In diffuse clouds, an interstellar radiation flux of about 8 × 10 7 photons cm −2 s −1 (Mathis et al 1983), combined with σ d,UV found by Mennella et al (2001), gives a characteristic destruction time by exposure to UV radiation t diffuse d,UV = 4 × 10 3 years, a time much shorter than for the destruction by cosmic rays. The destruction of the interstellar 3.4 μm feature in diffuse medium is thus most probably caused by the UV field in these regions rather than by CR interactions.…”

Section: Diffuse Interstellar Mediummentioning

confidence: 99%

“…The destruction of C-H bonds by UV irradiation has been studied by Muñoz Caro et al (2001) in hydrocarbon molecules and by Mennella et al (2001) in hydrocarbon grains. They found a destruction cross section σ d,UV = 1.0 × 10 −19 cm 2 /photon.…”

Section: Evolution Of the 34 μM Feature Between Diffuse And Dense Phmentioning

confidence: 99%

Ion irradiation of carbonaceous interstellar analogues

Godard

Féraud

Chabot

et al. 2011

A&A

108

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Context. A 3.4 μm absorption band (around 2900 cm −1 ), assigned to aliphatic C-H stretching modes of hydrogenated amorphous carbons (a-C:H), is widely observed in the diffuse interstellar medium, but disappears or is modified in dense clouds. This spectral difference between different phases of the interstellar medium reflects the processing of dust in different environments. Cosmic ray bombardment is one of the interstellar processes that make carbonaceous dust evolve. Aims. We investigate the effects of cosmic rays on the interstellar 3.4 μm absorption band carriers. Methods. Samples of carbonaceous interstellar analogues (a-C:H and soot) were irradiated at room temperature by swift ions with energy in the MeV range (from 0.2 to 160 MeV). The dehydrogenation and chemical bonding modifications that occurred during irradiation were studied with IR spectroscopy. Results. For all samples and all ions/energies used, we observed a decrease of the aliphatic C-H absorption bands intensity with the ion fluence. This evolution agrees with a model that describes the hydrogen loss as caused by the molecular recombination of two free H atoms created by the breaking of C-H bonds by the impinging ions. The corresponding destruction cross section and asymptotic hydrogen content are obtained for each experiment and their behaviour over a large range of ion stopping powers are inferred. Using elemental abundances and energy distributions of galactic cosmic rays, we investigated the implications of these results in different astrophysical environments. The results are compared to the processing by UV photons and H atoms in different regions of the interstellar medium. Conclusions. The destruction of aliphatic C-H bonds by cosmic rays occurs in characteristic times of a few 10 8 years, and it appears that even at longer time scales, cosmic rays alone cannot explain the observed disappearance of this spectral signature in dense regions. In diffuse interstellar medium, the formation by atomic hydrogen prevails over the destruction by UV photons (destruction by cosmic rays is negligible in these regions). Only the cosmic rays can penetrate into dense clouds and process the corresponding dust. However, they are not efficient enough to completely dehydrogenate the 3.4 μm carriers during the cloud lifetime. This interstellar component should be destroyed in interfaces between diffuse and dense interstellar regions where photons still penetrate but hydrogen is in molecular form.

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UV photodestruction of CH bonds and the evolution of the 3.4 $\mathsf{\mu}$m feature carrier

Cited by 101 publications

References 31 publications

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Mid-infrared spectroscopy of UV irradiated hydrogenated amorphous carbon materials

Spatially Resolved 3 Micron Spectroscopy of IRAS 22272+5435: Formation and Evolution of Aliphatic Hydrocarbon Dust in Proto–Planetary Nebulae

Ion irradiation of carbonaceous interstellar analogues

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