The electrons in atoms occupy atomic orbitals (AOs) that are represented as the regions around the nuclei where there is a high probability of finding the electrons. In the so-called LCAO (linear combitaks) approach, as pioneered by Hund and Mulliken, when AOs come close together, they overlap forming MOs (molecular orbitals). Two AOs can overlap to form two MOs, one of which lies at a lower energy level (BMO) than the other at a higher energy level and is called an antibonding molecular orbital (ABMO). Each MO can hold one or two electrons in accordance with Pauli’s exclusion principle. MOT can explain the paramagnetism of molecules such as O₂ and NO and other spectral features