For smaller species (typically 7 to 8 heavy atoms or less), the CCSD(T)-F12b/cc-pVnZ-F12 methods were used, and for larger species, the double-hybrid and dispersion-corrected density functional method, B2PLYP-D3(BJ), was used with the cc-pVnZ basis sets. Anharmonicity corrections (ANH) were computed using second-order vibrational perturbation theory (VPT2), implemented at the CCSD(T)/cc-pVnZ levels for smaller species and at the B2PLYP-D3(BJ)/cc-pVnZ levels for larger species. For species with torsional modes, the corresponding harmonic frequency was replaced and corrected by the one-dimensional hindered-rotor model, with internal rotation potentials evaluated at B2PLYP-D3(BJ)/cc-pVTZ.