Rotationally inelastic collisions of H₂⁺ ions with He buffer gas: Computing cross sections and rates

Area of Science:

• Chemical Physics
• Quantum Scattering Theory
• Atomic and Molecular Collisions

Background:

• Experiments aim to cool molecular ions internally using buffer gases in ion traps.
• Understanding inelastic collisions is key for achieving cryogenic temperatures for molecular ions.
• Hydrogen molecular ions (H2+) are fundamental systems for studying molecular collisions.

Purpose of the Study:

• To perform quantum calculations for inelastic collisions between H2+ ions and He atoms.
• To investigate state-changing rotational collisions and their rates.
• To analyze the impact of hyperfine and fine structure on collision dynamics.

Main Methods:

• Ab initio quantum calculations of the potential energy surface.
• Solving coupled channel quantum scattering equations.
• Investigating hyperfine and fine structure effects.

Main Results:

• Calculated state-changing rotationally inelastic cross sections for H2+ + He collisions.
• Compared collision dynamics with and without hyperfine/fine structure.
• Determined temperature-dependent inelastic rates and collisional efficiency.

Conclusions:

• Provides essential data for modeling experiments with internally cold molecular ions.
• Highlights the role of He buffer gas in deactivating internal rotational populations.
• Offers insights into propensity rules for rotational state changes in H2+ + He collisions.