I have been reading Molecular Orbitals and Organic Chemical Reactions (Student Edition) by Ian Fleming. On Pg 5, Fleming mentions that the diatomic helium molecule cannot exists because there is an overall energy increase from populating both the bonding and antibonding molecular orbitals equally (i.e. putting 2 electrons into each). However, why should there be a larger absolute energy difference between the antibonding MO and the atomic orbitals compared to the energy difference between the bonding MO and atomic oritals? Fleming explains this by saying that this is due to the presence of inter-electronic repulsion in the MOs as there are two electrons present in each MO. This may seem to make sense.
However, in most MO diagrams, the energy levels of the bonding and antibonding MOs are drawn equidistant away from the energy level of the atomic orbitals. Does there seem to be a contradiction?
It is not a duplicate as I am proposing a new explanation of "inter-electronic repulsion upon population of the MOs", which has never been discussed before.