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

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, C2v 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.