New Full-Dimensional Reactive Potential Energy Surface for the H₄ System

Area of Science:

• Astrochemistry
• Chemical Physics
• Quantum Dynamics

Background:

• Hydrogen molecules (H₂) are abundant in the universe, making H₂ collisions vital for astrochemistry.
• Understanding H₂ + H₂ collisions serves as a benchmark for few-body dynamics methods.

Purpose of the Study:

• Develop a highly accurate, full-dimensional potential energy surface (PES) for the H₂ + H₂ system.
• Incorporate all reactive channels for comprehensive dynamic studies.

Main Methods:

• Calculated 39,538 new ab initio points at the MRCI/AV5Z level for reactive channels.
• Developed a global PES using a permutation invariant polynomial neural network (PIP-NN) with 79,000 total points.
• Utilized quasi-classical trajectory studies to analyze reaction dynamics.

Main Results:

• Achieved high fidelity representation of the PES with RMSE = 0.6 meV.
• The PIP-NN PES accurately describes collision-induced dissociation, single-exchange, and four-center exchange reactions.
• Preliminary studies showed significant vibrational enhancement across all reaction channels.

Conclusions:

• The new PIP-NN PES provides a robust tool for studying H₂ + H₂ reactive collisions.
• Vibrational enhancement plays a key role in the dynamics of these fundamental reactions.
• This work advances the understanding of molecular collisions in astrochemistry and theoretical chemistry.