Accurate global adiabatic potential energy surfaces for three low-lying electronic states of AlH2 free radicals

Abstract

In order to obtain the all-round molecular properties of the AlH₂ system and the corresponding dynamical characteristics of the Al + H₂ (v = 0, j = 0) → H + AlH reaction, three significant global adiabatic potential energy surfaces of AlH₂ (X²A₁, ²B₁, and ²B₂) free radicals were constructed for the first time. Ab initio energies were calculated under the multi-reference configuration interaction method and the aug-cc-pV(T,Q)Z basis sets; then the ab initio energies were extrapolated to the complete basis sets limit. The three adiabatic potential energy surfaces were constructed by the many-body expansion theory. The maximum root-mean square error was just 50 cm⁻¹, which was small enough to ensure that the potential energy surfaces were accurate. The concerned T-type insertion topographical features, dissociation schemes, C_2v geometry reaction mechanisms, and minimum energy curve paths were investigated and are discussed in detail. Several differences from previous studies are also pointed out. Eventually, the integral cross-sections of Al + H₂ (v = 0, j = 0) → H + AlH reaction as calculated by quasi-classical trajectory method were employed to predict the dynamical properties of AlH₂, providing the most reliable theoretical reference of the dynamical characteristics known thus far for such a reaction. These new potential energy surfaces can be treated as a reliable basis for investigation of the dynamics and as a component for constructing larger aluminum-/hydrogen-containing systems.