[mana]

hi all
how I can get the energy level of different MO orbitals in O2 and other molecules?

[Enthalpy]

Hi Mana, could you detail your intention in "get the energy level"?

The purpose of such diagrams is essentially a qualitative explanation. Show the more electrons find a lower energy level, that some are unpaired, that the bond in O₂ is less strong than in N₂, and so on. Very useful if you seek understanding rather than an enthalpy of formation.

Computing energies by hand quickly from simple rules, no. This needs heavy software, which has nice successes.