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The interstellar chemistry of PAH cations
T P Snow1, V Le Page, Y Keheyan
1Center for Astrophysics and Space Astronomy, University of Colorado, Boulder 80309, USA. tsnow@casa.colorado.edu
Nature
|January 24, 1998
Summary
Diffuse interstellar bands (DIBs) may not originate from polycyclic aromatic hydrocarbon (PAH) cations. Laboratory studies show these cations are too reactive, suggesting protonated PAHs are more likely sources of DIBs.
Area of Science:
- * Astrochemistry
- * Molecular Spectroscopy
- * Interstellar Medium
Background:
- * Diffuse interstellar bands (DIBs) are unexplained absorption features in starlight.
- * Polycyclic aromatic hydrocarbons (PAHs) are abundant in space and proposed as DIB carriers.
- * Previous lab studies suggested ionized PAHs might cause DIBs, but identification remained elusive.
Purpose of the Study:
- * To investigate the gas-phase chemical reactivity of specific polycyclic aromatic hydrocarbon (PAH) cations.
- * To assess the stability and interstellar abundance of PAH cations.
- * To guide future searches for the molecular carriers of DIBs.
Main Methods:
- * Gas-phase laboratory experiments involving PAH cations (C6H6+, C10H8+, C16H10+).
- * Chemical reactivity studies under simulated interstellar conditions.
- * Analysis of reaction products and stability.
Main Results:
- * PAH cations (C6H6+, C10H8+, C16H10+) exhibit high chemical reactivity in the gas phase.
- * These reactive PAH cations are unlikely to persist in significant abundances in the interstellar medium.
- * Rapid reaction with hydrogen was observed for the studied PAH cations.
Conclusions:
- * The high reactivity of PAH cations challenges their role as direct carriers of diffuse interstellar bands (DIBs).
- * Protonated PAH cations, formed from reactions with hydrogen, are proposed as more plausible candidates for DIB carriers.
- * Future research should focus on identifying DIBs with protonated PAH cations and related species.