What is the order of bond enthalpies of halogens? Why is it not opposite to that of bond lengths?

Explanation

Bond lengths of halogens are in the order :
`F_(2)ltCl_(2)ltBr_(2)ltI_(2)`.

Bond energies are expected in the order :
`F_(2)ltCl_(2)ltBr_(2)ltCl_(2)`.
But the experimental bond enthalpies are :
`Cl_(2)gtBr_(2)gtF_(2)gtI_(2)`.
Bond enthalpy of `F_(2)` is very less , because lone pair lone pair repulsions are appreciable in `F_(2)` as the bond length is small in `F_(2)`.
It was also thought , though not appropriate , that F-F bond is weak as multiple bond is not possible with no d-orbitals in the valence shell of fluorine .