Hello. I'm now working in the spectroscopy and I'm wondering in one instantaneous moment of ionization. Let's have an atom with multiple bound electrons. The external energy (like in form of photon) is introduced on the atom such that outer bound electron is ionized and the question emerges. What happens on un-ionized bound electrons? One electron is now missing and the Hamiltonian of the system have to be modified such that new bound states according to new Hamiltonian should be established. Just before ionization, all electrons were occupying the old bound state which were determined by the old Hamiltonian, the Hamiltonian before ionization. Does that mean there is instantaneous transition from old states to new states for the remaining electrons? It doesn't make sense the energy levels of new states are higher than old states. It is also impossible that new states are identical to the old states since the new Hamiltonian differs from old one. The only way for bound electrons to go is to transition to the new states which energy levels are lower than one ones and there must be additional energy release from this transition. Am I right? If that is true, we can capture the moment of the ionization by observing spectrum coming from such a instantaneous transition just after ionization.