Figure 1. EP maps, electronic properties and frontier MOs of the ground state CO (X ¹Σ⁺) and the first excited triplet state CO^t (a ³Π).

EP maps for the ground (a) and first excited ((b) top and (c) front views) states of CO at the MP2/aVTZ level (density isovalue: 0.001 au). Bond-length (d in pm), dipole moment (μ_z in D), and quadrupole moment (Q_zz in D⁺Å) are given at the CCSD(T)/aV5Z level. For the singlet CO, both C and O atom-ends show negative EP, whereas the cylindrical surface of the CO bond, positive EP. For CO^t, the C atom-end gives positive EP, whereas the O atom-end, negative EP. MO energies and orbital shapes for (d) CO and (e) CO^t are given at the M06-2X/aVTZ level.