The hydrogen molecular ion {rm H_2^1}, with one electron and two protons, is the simplest molecule. The equilibrium spacing between the protons is 0.11 {rm nm}. Suppose the electron is at the midpoint between the protons and moving at 1.5 times 10^6 {rm m/s} perpendicular to a line between the protons.
How far (in {rm nm}) does the electron move before reaching a turning point? Because of their larger mass, the protons remain fixed during this interval of time. Note, that an accurate description of {rm H_2^1} requires quantum mechanics. Even so, a classical calculation like this provides some insight into the molecule.