Calculations of rate constants for the three-body recombination of H2 in the presence of H2

We construct a new global potential energy hypersurface for H2+H2 and perform quasiclassical trajectory calculations using the resonance complex theory and energy transfer mechanism to estimate the rate of three-body recombination over the temperature range 100–5000 K. The new potential is a faithful representation of ab initio electronic structure calculations, is unchanged under the operation of exchanging H atoms, and reproduces the accurate H3 potential as one H atom is pulled away. Included in the fitting procedure are geometries expected to be important when one H2 is near or above the dissociation limit. The dynamics calculations explicitly include the motion of all four atoms and are performed efficiently using a vectorized variable-stepsize integrator. The predicted rate constants are approximately a factor of 2 smaller than experimental estimates over a broad temperature range.