Theoretical characterization of the disilaethynyl anion (Si2H−)

Abstract

The singlet-state potential energy surface of the disilaethynyl anion (Si2H−) has been investigated using ab initio self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory with large basis sets. Four stationary points [cyclic (monobridged) A11 (C2v), linear Σ1 + (C∞v), bent A′1 (Cs), and quasilinear Σ1 + (Cs) structures] were located with the correlated wave functions, while only two stationary points [cyclic (monobridged) A11 (C2v) and linear Σ1 + (C∞v) structures] were found with the SCF method. The cyclic structure (C2v) is predicted to be the global minimum at all levels of theory. The linear structure (C∞v) is found to be a transition state between the two quasilinear structures (Cs) at the correlated levels of theory, while the SCF linear structure is predicted to be a transition state between the two cyclic structures. The quasilinear structure possesses a Si–Si–H bond angle similar to that of the monobridged Si2H2 molecule. The bent geometry is assigned to a transition state for the isomerization reaction between the cyclic and quasilinear structures. With the most reliable level of theory, augmented correlation-consistent polarized valence quadruple-ζ CCSD(T), the quasilinear structure is predicted to be 8.6 kcal/mol [7.9 kcal/mol with the zero-point vibrational energy (ZPVE) correction] above the cyclic (monobridged) structure, and the energy barrier for the cyclic→quasilinear isomerization reaction is determined to be 12.1 kcal/mol (11.0 kcal/mol with the ZPVE correction). The inversion reaction between the quasilinear and linear structures is found to have a very small energy barrier. With the estimated aug-cc-pCVQZ CCSD(T) method the electron affinity of Si2H is predicted to be 2.31 eV, which is in excellent agreement with the experimental value 2.31±0.01 eV.