Quantum Effects in Cold Molecular Collisions from Spatial Polarization of Electronic Wave Function.

Area of Science:

• Quantum Chemistry
• Chemical Physics
• Atomic and Molecular Collisions

Background:

• Quantum phenomena, including electronic and nuclear resonances, manifest as structures in measured cross sections.
• Recent cold chemistry experiments observed such structures in collisions of ground-state hydrogen isotopologues (H2/HD) with excited helium atoms (He(23P)).
• A theoretical explanation for these observed structures was previously lacking.

Purpose of the Study:

• To provide a quantum theoretical explanation and simulation for the structures observed in the He(23P) + H2/HD cold chemistry experiment.
• To elucidate the underlying physical mechanisms responsible for the resonance structures in reaction rate coefficients.

Main Methods:

• Utilized ab initio calculations to incorporate complex potential energy surfaces.
• Employed adiabatic variational theory to simplify the multidimensional scattering problem.
• Reduced the scattering process to a series of uncoupled one-dimensional (1D) scattering simulations.

Main Results:

• The theoretical simulations achieved remarkable agreement with experimental data.
• Identified the spatial arrangement of the excited helium p-orbitals relative to the interaction axis as the cause of the observed structures.
• Demonstrated a transition from a two-rotor model to a three-rotor model due to orbital orientation.

Conclusions:

• The study successfully explains the origin of resonance structures in the reaction rate coefficient for He(23P) + H2/HD collisions.
• The developed theoretical framework provides a method to explain and predict cross sections and reaction rate coefficients for resonance-related phenomena.
• Highlights the importance of orbital dynamics in understanding complex chemical reaction pathways.