Electronically Nonadiabatic Dynamics of O2 + O Collisions on Sixteen New Machine-Learned 3 A ″ Global Potential Energy Surfaces

Abstract High-energy O2 + O collisions on the 3A″ potential surface manifold of O3 provide a challenge for multistate nonadiabatic dynamics because covalent valence states and ionic configurations become strongly mixed in dynamically accessible regions. We developed a global machine-learned compatible potential-energy matrix (CPEM) for a 16-state nonadiabatic description of O2(X) + O(3P) dynamics with 3A″ symmetry, trained on XMS-CASPT2 data and augmented with physically motivated treatments of O2+ + O– ionic character where they are important. The adiabatic surfaces obtained by diagonalization have the analytic gradients and the correct conical-intersection topology, and they achieve good accuracy in both triatomic and O2 + O asymptotic limits. This establishes a general strategy for learning dense manifolds of coupled potential-energy surfaces with mixed covalent–ionic character. Using these surfaces with the asymptotically extended curvature-driven coherent switching with decay of mixing (AE-κCSDM) dynamics method, we computed electronically inelastic and reactive cross sections over a wide range of translational energies and O2 rovibrational states. The simulations reveal exchange reactivity, modest electronically nonadiabatic branching, and systematic trends in electronic-state-resolved excitation as functions of vibrational quantum number, rotational excitation, and dynamical energy.