The H2 (v′, J′) partial reaction cross sections arising from collisions of 1.3 eV H atoms with HI have been measured using coherent anti-Stokes Raman scattering (CARS) spectroscopy. Quasiclassical trajectory (QCT) calculations on a representative potential energy surface have been used to simulate the dynamics of this reaction. Comparison of the QCT and experimental results shows good agreement in average energy disposal, total cross section, and rotational state distributions. The only significant disagreement is in the detailed vibrational state distribution, for which the calculations give monotonically decreasing population with increasing v′, while the experimental results show a significant population inversion between v′ = 0 and v′ = 1. Based on the QCT-experiment comparison we make suggestions for improving the H + HI potential energy surface. © 1992 American Institute of Physics.