Stability of the CH₃Cl dication Available to Purchase

The chloromethane cation and dication have been studied using the complete active space self‐consistent field method followed by a multireference perturbative configuration interaction. The ²E ground state of CH₃Cl⁺ presents a weak Jahn–Teller distortion, the ²A′ and ²A″ components being separated by only 3.4 kcal/mol with very similar geometries. Both states are equilibrium structures. Contrary to previous calculations, the lowest singlet and triplet states of CH₃Cl⁺⁺ are calculated to be stable. While the ³A₂ state keeps the neutral C_3v symmetry, the ¹E singlet state shows a large Jahn–Teller effect, with a splitting of 32.7 kcal/mol in favor of the ¹A′ state, which is the ground state of the molecule. The planar ¹A′ state of CH₂ClH⁺⁺ is found to be the most stable isomer, lying 41.4 kcal/mol below the corresponding state of CH₃Cl⁺⁺. The ³A″ state, which lies 22.59 kcal/mol above the ¹A′ state, has a nonplanar C_s‐symmetry geometry. Finally, the CH₃Cl⁺⁺ (¹A′)→CH₂ClH⁺⁺ (¹A′) isomerization takes place via a C₁‐symmetry transition state, with an energy barrier of 32.85 kcal/mol.