The tunneling splittings of the ground state and some excited vibrational states for the inversion motion in H3C− anion and H3Si radical

Abstract

Splitting of the ground state and some excited symmetric bending vibrational states due to inversion tunneling in the H₃C⁻ anion and H₃Si radical is analyzed by numerically solving the vibrational Schrödinger equation of restricted (2D) dimensionality. We used the following two vibrational coordinates for the H₃X structure (X = C, Si): the distance of the X atom from the plane of a regular triangle formed by three hydrogen atoms (1) and a symmetry coordinate composed of three distances between chemically non-bonded hydrogen atoms (2). The kinetic energy operator in this case takes the simplest form. The 2D potential energy surface (PES) in the given coordinates was calculated for H₃C⁻ at the CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, CCSD(T)/aug-cc-pV5Z, CCSD(T)/CBS(TQ5), CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/t-aug-cc-pVTZ, and CCSD(T)/q-aug-cc-pVTZ levels of theory, based on recommendations from recently published work [M.C. Bowman, B. Zhang, W.J. Morgan, H.F. Schaefer III, Mol.Phys., 117 (2019) 1069–1077]. The same 2D PES for the H₃Si radical was calculated at the CCSD(T)/aug-cc-pVDZ CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ, and CCSD(T)/CBS(D,T,Q) as well as at the CCSD(T)/d-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVTZ, CCSD(T)/un-aug-cc-pVQZ levels of theory. The tunneling splittings for the D₃C⁻ anion and D₃Si radical were calculated as well. The results of calculations demonstrate good agreement with available experimental data on umbrella vibration frequencies and inversion splittings for the title molecules.