Geometries and potential energy curves of InSb2, SbIn2, GaAs2, AsGa2, and their ions

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Abstract
Complete active space self-consistent field calculations (CASSCF) are carried out on the potential energy curves of three electronic states (2B2, 2A1, and 2B1) of InSb2 and GaAs2, the 1A1 state of InSb+2, seven electronic states of SbIn2, and six electronic states of SbIn+2. In addition, permutational isomers of AsGa2, GaAs2, and InSb2 are investigated. We use multireference singles+doubles CI calculations to optimize the equilibrium geometries and to compute the dissociation energies of all these species. The ground states of InSb2 and SbIn2 were found to be of 2B2 and 2B1 symmetries, respectively, with isosceles triangular geometries. The linear permutational isomer, In–Sb–Sb was found to be 16 kcal/mol above the bent isosceles triangular structure. We find that AsGa2 and GaAs2 also to have permutational isomers ∼16 kcal/mol above the bent (C2v) structures. However, the linear permutational isomers convert to the more stable bent isosceles triangular forms without barriers. The ground states of InSb+2 and SbIn+2 were found to be 1A1 with isosceles triangular geometry and 3Σ−g with linear geometry, respectively. The atomization energies and ionization potential of InSb2 are computed as 4.42 and 5.83 eV, respectively, while the corresponding values for SbIn2 are 2.73 and 5.65 eV, respectively. The atomization energy of AsGa2 is 3.7 eV. The ground state InSb2 (GaAs2) exhibits enhanced Sb–Sb (As–As) bonding, while the ground state of SbIn2 (AsGa2) exhibits enhanced In–Sb (Ga–As) bonding and nonbonding interactions between In (Ga). Our theoretical calculations of mixed III–V trimers explain the experimental relative abundance of trimers and odd–even alternation in the IPs observed by O’Brien et al. [J. Chem. Phys. 84, 4074 (1986)] for GaxAsy (x+y=3).