Threshold energies for single-carbon knockout from polycyclic aromatic hydrocarbons.

Area of Science:

• Physical Chemistry
• Chemical Physics
• Atomic and Molecular Collisions

Background:

• Polycyclic Aromatic Hydrocarbons (PAHs) are crucial in interstellar chemistry.
• Understanding ion-molecule interactions is vital for astrochemistry and materials science.
• Previous studies lacked precise measurements of carbon knockout dynamics in isolated PAH cations.

Purpose of the Study:

• To measure absolute cross sections for single-carbon knockout from PAH cations.
• To determine experimental and simulated knockout threshold energies.
• To investigate energy transfer dynamics in high-energy collisions.

Main Methods:

• Experimental measurement of absolute cross sections for ultrafast (femtosecond) carbon knockout.
• Classical molecular dynamics (MD) simulations covering collision energies from 10 eV to 105 eV.
• Analysis using a simple analytical expression to model cross-section shapes.

Main Results:

• Absolute cross sections for carbon knockout were measured as a function of collision energy (10–200 eV).
• Experimental and MD simulations yielded threshold energies of 32.5 ± 0.4 eV and 41.0 ± 0.3 eV, respectively.
• Deduced displacement energies (TdispSE = 23.3 ± 0.3 eV, TdispMD = 27.0 ± 0.3 eV) align with graphene displacement energies.

Conclusions:

• First measurements of knockout threshold energies for isolated molecular cations.
• The study provides critical data for modeling carbon knockout in PAHs.
• Results validate simulation methods and offer insights into fundamental collision processes.