Plasma generation and processing of interstellar carbonaceous dust analogs

Area of Science:

• Astrochemistry
• Materials Science
• Plasma Physics

Background:

• Interstellar dust composition is crucial for understanding star and planet formation.
• Amorphous hydrogenated carbon (a-C:H) is a relevant analog for interstellar dust.
• Previous studies have explored a-C:H properties, but discrepancies in characterization methods persist.

Purpose of the Study:

• To synthesize and characterize a-C:H interstellar dust analogs.
• To investigate the effects of energetic processing (electron irradiation) on a-C:H.
• To assess the role of cosmic rays in modifying interstellar dust properties.

Main Methods:

• Plasma deposition of a-C:H using CH4 + He mixtures.
• Characterization via SEM, IR spectroscopy, and UV-visible reflectivity.
• Density Functional Theory (DFT) calculations for structural and spectral analysis.
• Energetic processing using 5 keV electron beams.

Main Results:

• Successful synthesis of a-C:H samples with high hydrogen content (≈50%).
• Discrepancies observed in sp2/sp3 carbon hybridization ratios between IR and reflectivity measurements.
• Electron irradiation induced dehydrogenation and graphitization, evidenced by changes in IR spectra.
• The rate of CH band decay upon electron irradiation suggests cosmic rays alone are insufficient to explain observed changes in dense interstellar clouds.

Conclusions:

• a-C:H samples serve as viable analogs for interstellar dust.
• Discrepancies in characterization highlight the complexity of a-C:H analysis.
• Energetic processing significantly alters a-C:H structure, mimicking some aspects of space weathering.
• Cosmic ray bombardment may not be the sole driver for the observed spectral evolution of interstellar dust in dense environments.