FeO double-well potential as a result of spin density redistribution

According to the calculation of the electron structure of the FeO molecule performed by the ZINDO1 semi-empirical technique, the ground-state adiabatic potential has two close minima, each containing one vibration level. The states of the system in this minima differ in the spatial distribution of the spin density: the spin density is centered in the iron atom in the lowest well at 1.95 Å and a fraction of the spin with the opposite sign is transferred to oxygen in the other well at 1.8 Å. The temperature dependence of the fractions of molecules with the different bond lengths in the FeO gas has been found. The probability of switching the spin states has been shown to increase with pressure and temperature.