Contraction of diatomic molecules upon chemisorption

On the basis of self-consistent model calculations for H₂ standing upright on a jellium surface it is shown that contraction of a molecular bond is possible upon chemisorption in spite of a weakened intramolecular interaction. This leads us to point out the possibility of a reduced bond length for CO on Ni (100). A large enough reduction would make the recent conflicting LEED and angular resolved UPS data for this system compatible.