energy level after photon absorbtion

Johnahh

Say a photon was absorbed by an electron at 1s in an oxygen atom but it only had enough energy to move it to another energy level that was already occupied such a 2s etc. What happens to this photon?

mfb

The photon does not get absorbed if there is no available unoccupied energy level for the electron.

Johnahh

so how does the electron know that the photon does not have enough energy to move it to a free orbital?

mfb

Quantum mechanics. If a process is impossible, it just does not happen.