Potential energy surfaces of CH+4

The potential energy surfaces of the three lowest electronic states of CH+4 are calculated. CI calculations based on average natural orbitals from preliminary multireference singles and doubles CI calculations are found to provide a balanced description of the three states. The calculated points are fit to the eigenvalues of a 3×3 matrix whose elements are a power-series expansion in the normal-mode displacements from the SCF tetrahedral geometry. The equilibrium structures for the C2v, D2d, and C3v Jahn–Teller distortions are located and the vibrational frequencies for these structures are calculated. In addition, the transition state for the pseudorotation between equivalent C2v minima is located and the nature of the pseudorotation is discussed in detail.