HYDROGEN UPTAKE BY AN ALKALI-METAL ION

Quantum-chemical calculations including correlations have been carried out to study the amount and nature of hydrogen uptake by a Li atom in neutral as well as in ionic form. We have found that while the neutral Li atom cannot bind more than one hydrogen atom, the cation can bind a large number of hydrogen atoms in molecular form. This contrasting behavior originates from the fact that the bonding of hydrogen with neutral Li is covalent while that with the cation is primarily caused by polarization. The bonding of hydrogen with the Li- ion exhibits dual nature. The first H-2 molecule binds to the anion dissociatively while the subsequent H-2 molecule can only exist in <<physisorbed>> state.