The Effect of Cluster Size on the Intra-Cluster Ionic Polymerization Process.

Area of Science:

• Astrochemistry
• Physical Chemistry
• Computational Chemistry

Background:

• Polyaromatic hydrocarbons (PAHs) are prevalent in the interstellar medium (ISM).
• Understanding PAH formation, particularly benzene (a PAH building block), is crucial.
• Ionization of neutral clusters can trigger intra-cluster ionic polymerization and molecular growth.

Purpose of the Study:

• To investigate the effect of larger acetylene clusters on molecular growth via ionization.
• To determine if clusters beyond six units yield increased C6H6+ production.
• To explore aggregation limits and identify novel species formed under simulated ISM conditions.

Main Methods:

• Ab-initio molecular dynamics (AIMD) simulations were employed.
• Simulations modeled the ionization of acetylene clusters containing 10 and 20 units.
• Analysis focused on aggregation processes and resulting molecular structures.

Main Results:

• Maximum aggregation of up to four acetylene units was observed, forming bonded C8H8+ species.
• Bicyclic C8H8+ species were identified, suggesting potential for astrochemical detection.
• Reactivity rates were comparable for both 10 and 20 acetylene cluster simulations.

Conclusions:

• Larger acetylene clusters facilitate the formation of C8H8+ species, expanding on previous findings.
• The identification of bicyclic C8H8+ provides a new target for astrochemical observations.
• Ionization of acetylene clusters is a viable pathway for PAH precursor formation in the ISM.