Quasiclassical trajectory calculations of hydrogen absorption in the (NaAlH4)2Ti system on a model analytical potential energy surface

Abstract

We performed a quasiclassical trajectory dynamics study on a model analytical 21-dimensional (7 active atoms) potential energy surface (PES) to examine in detail the mechanism of the hydrogen absorption in a simple (NaAlH₄)₂Ti model system. The reaction involves a capture of H₂ by the Ti centre and formation of the (η²-H₂)Ti(NaAlH₃)₂ coordination complex containing the side-on bonded dihydrogen ligand. The calculated rate constant corresponds to a very fast capture of H₂ by the Ti coordination sphere without a demonstrable barrier. This implies that this step is not the rate-determining step in the complex multi-step process of the NaAlH₄ recovery. The model analytical PES captures the essence of this reaction well and the corresponding energy contours compare favourably to those based on the all-atom hybrid density functional theory calculations.