Dissociative Electron Attachment to the HNC_{3} Molecule

Area of Science:

• Astrochemistry
• Quantum Chemistry
• Theoretical Chemistry

Background:

• Negative molecular ions are crucial in interstellar chemistry.
• Understanding their formation pathways is essential for astrochemistry.
• Dissociative electron attachment (DEA) and radiative electron attachment (REA) are key formation mechanisms.

Purpose of the Study:

• To theoretically model the dissociative electron attachment to HNC3.
• To compute the cross section and rate coefficient for this DEA process.
• To compare the efficiency of DEA with REA for producing negative molecular ions in interstellar space.

Main Methods:

• First-principles theoretical modeling of electron-molecule collisions.
• Analysis of low-energy resonances in HNC3 + e- interactions.
• Calculation of DEA cross sections and rate coefficients.

Main Results:

• A low-energy, repulsive resonance in HNC3 + e- collisions was identified.
• The HNC3- anion was found to dissociate to C3N- + H without a potential barrier.
• The computed DEA rate coefficient at 300 K is 5x10^-9 cm^3/s.

Conclusions:

• DEA to HNC3 is significantly more efficient (three orders of magnitude) than REA at producing negative molecular ions.
• DEA is proposed as the dominant mechanism for forming observed negative molecular carbon-chain ions in the interstellar medium.
• This finding has implications for understanding the chemical evolution of interstellar clouds.