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Title: HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND

Abstract

The effects of cosmic rays on the carriers of the interstellar 3.4 μ m absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH{sub 3} and CH{sub 2} in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH{sub 3} and CH{sub 2} by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity versus electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H{sub 2} molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher-energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic-ray destruction times for the 3.4 μ m bandmore » carriers lie in the 10{sup 8} yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 10{sup 7} yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.« less

Authors:
; ; ; ;  [1]
  1. Instituto de Estructura de la Materia, IEM-CSIC, Serrano 123, E-28006 Madrid (Spain)
Publication Date:
OSTI Identifier:
22667271
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 831; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ATOMS; CARBON; COSMIC DUST; COSMIC RADIATION; DECAY; DEHYDROGENATION; ELECTRON BEAMS; ELECTRONS; HYDROGEN; HYDROGENATION; INTERSTELLAR SPACE; IONS; IRRADIATION; KEV RANGE; LIFETIME; MOLECULES; RECOMBINATION; SIMULATION; ULTRAVIOLET RADIATION

Citation Formats

Maté, Belén, Molpeceres, Germán, Jiménez-Redondo, Miguel, Tanarro, Isabel, and Herrero, Víctor J. HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND. United States: N. p., 2016. Web. doi:10.3847/0004-637X/831/1/51.
Maté, Belén, Molpeceres, Germán, Jiménez-Redondo, Miguel, Tanarro, Isabel, & Herrero, Víctor J. HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND. United States. doi:10.3847/0004-637X/831/1/51.
Maté, Belén, Molpeceres, Germán, Jiménez-Redondo, Miguel, Tanarro, Isabel, and Herrero, Víctor J. Tue . "HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND". United States. doi:10.3847/0004-637X/831/1/51.
@article{osti_22667271,
title = {HIGH-ENERGY ELECTRON IRRADIATION OF INTERSTELLAR CARBONACEOUS DUST ANALOGS: COSMIC-RAY EFFECTS ON THE CARRIERS OF THE 3.4 μ m ABSORPTION BAND},
author = {Maté, Belén and Molpeceres, Germán and Jiménez-Redondo, Miguel and Tanarro, Isabel and Herrero, Víctor J.},
abstractNote = {The effects of cosmic rays on the carriers of the interstellar 3.4 μ m absorption band have been investigated in the laboratory. This band is attributed to stretching vibrations of CH{sub 3} and CH{sub 2} in carbonaceous dust. It is widely observed in the diffuse interstellar medium, but disappears in dense clouds. Destruction of CH{sub 3} and CH{sub 2} by cosmic rays could become relevant in dense clouds, shielded from the external ultraviolet field. For the simulations, samples of hydrogenated amorphous carbon (a-C:H) have been irradiated with 5 keV electrons. The decay of the band intensity versus electron fluence reflects a-C:H dehydrogenation, which is well described by a model assuming that H{sub 2} molecules, formed by the recombination of H atoms liberated through CH bond breaking, diffuse out of the sample. The CH bond destruction rates derived from the present experiments are in good accordance with those from previous ion irradiation experiments of HAC. The experimental simplicity of electron bombardment has allowed the use of higher-energy doses than in the ion experiments. The effects of cosmic rays on the aliphatic components of cosmic dust are found to be small. The estimated cosmic-ray destruction times for the 3.4 μ m band carriers lie in the 10{sup 8} yr range and cannot account for the disappearance of this band in dense clouds, which have characteristic lifetimes of 3 × 10{sup 7} yr. The results invite a more detailed investigation of the mechanisms of CH bond formation and breaking in the intermediate region between diffuse and dense clouds.},
doi = {10.3847/0004-637X/831/1/51},
journal = {Astrophysical Journal},
number = 1,
volume = 831,
place = {United States},
year = {Tue Nov 01 00:00:00 EDT 2016},
month = {Tue Nov 01 00:00:00 EDT 2016}
}