In the molecule, each atom has one electron and both electrons
always settle into the lowest energy state of the molecule. Use your
result for Problem 17 to show that, to lowest order, the
the energy of the molecule lowers as the two molecules approach
each other at distance 2b as compared to the energy of the molecule
when the atoms are infinitely far apart ( 
).
Give a first order estimate for this ``bonding'' energy.
Note: Chemists refer to this lowest energy even state as a ``bond.''