On Your Marks, Get Set...

摘要

The firing of the starting pistol sets the runners out of their blocks and hurtling down the racetrack, and the race is often over in a blink of an eye. In the process of photoionization, photons with the right energy impinging on an atom will release an electron and leave behind a positively charged ion. Unlike the runners all lined up in a row, electrons are packed into atoms in a certain order, filling up different energy levels, generally the lowest first.