Middle panel: minimum energy path for the HCN/HNC isomerization for the first 12 ¹A′ (red) and 9 ¹A″ (blue) electronic states of HCN obtained using the PESs as described in the text. In black are the MEPs for the HCN⁺/HNC⁺ corresponding to the first ²A′ and ²A″ electronic states of the cation. The points correspond to PESs calculated previously. The left and right panels show the molecular orbital amplitudes of HCN (left panel) and HNC (right panel). Note that the molecular orbitals are ordered by the occupation number, not their energy.