This is a question in "Chemical Principles, 6th Edition, Steven Zumdahl": Bond energy has been defined in the text as the amount of energy required to break a chemical bond, so we have come to think of the addition of energy as breaking bonds. However, in some cases the addition of energy can cause the formation of bonds. For example, in a sample of helium gas subjected to a high-energy source, some He2 molecules exist momentarily and then dissociate. Use MO theory (and diagrams) to explain why He2 molecules can come to exist and why they dissociate. And this is from the solutions manual: The ground state MO electron configuration for He2 is (σ1s)2(σ1s*)2 giving a bond order of 0. Therefore, He2 molecules are not predicted to be stable (and are not stable) in the lowest energy ground state. However, in a high-energy environment, electron(s) from the antibonding orbitals in He2 can be promoted into higher-energy bonding orbitals, thus giving a nonzero bond order and a “reason” to form. For example, a possible excited-state MO electron configuration for He2 would be (σ1s)2(σ1s*)1(σ2s)1, giving a bond order of (3 – 1)/2 = 1. Thus excited He2 molecules can form, but they spontaneously break apart as the electron(s) fall back to the ground state, where the bond order equals zero. What do you think about the solution? I think it's incorrect.