Hi all. I'll starting a little research for my college assignment. But I need to discuss a few concepts in Quantum Mechanics [sorry for my english]. 1. I want to analyze perturbation effect that suffered by an ion. Is Rayleigh-Schrodinger theory suitable for this problem? if not, which suitable theory for it? 2. If an electromagnetic wave is passed to a atom, it will be absorbed by an electron and then emitted a photon when back to old level energy. So, where will the photon go (if a chain reaction is not exist)? is will merge with the electromagnetic wave or? Thank you.