The potential energy of two atoms in a molecule can sometimes be approximated by the morse function, u (r) = are(r-01.5 — 1)2 where r is the distance between the two atoms and a, r, and s are positive constants with s < < r. sketch this function for 0 < r < cc. find the equilibrium separation rip , at which u (r) is minimum. now write r = rox so that x is the displacement from equilibrium, and show that, for small displacements, u has the approximate form u = const kx 2 . that is, hooke's law applies. what is the force constant k?