Abstract
<jats:p>A full-dimensional potential energy surface (PES) is developed for H2O–N2 collisions to enable state-resolved simulations under high-temperature, nonequilibrium conditions. A total of 81,447 configurations were calculated using coupled-cluster singles, doubles, and perturbative triples with explicit correlation [CCSD(T)-F12a] and the aug-cc-pVTZ basis set; the resulting energies were fitted using the permutation invariant polynomial-neural network (PIP-NN) approach. The resulting PES has an overall root-mean-square error (RMSE) of 18.7 meV and an error of 6.6 meV for configurations below 5 eV, while accurately reproducing stationary structures and asymptotic behavior. Quasi-classical trajectory calculations were then performed for the vibrational relaxation of N2(v = 1, 2) by H2O between 1000 and 3000 K. The N2(v = 1 → 0) rate coefficient is approximately 2.0 × 10-12 cm3 molecule-1 s-1, whereas the v = 2 → 1 channel is about one order of magnitude slower and has greater statistical uncertainty. Energytransfer analysis indicates efficient vibration-rotation redistribution within H2O and predominantly forward-scattering dynamics. The PES provides a platform for state-resolved modeling of high-temperature molecular energy transfer.</jats:p>