Molecular Rydberg states are atomic-like states of molecules when an electron is

Question

Molecular Rydberg states are atomic-like states of molecules when an electron is distant (excited) or shielded enough from the molecular details. Electrons in this 9. type of state experience an effective positive charge of the molecule and thus can be described using the simple hydrogen atom model. NH4 (not the cation) is a very short-lived species which shares properties with atomic sodium particular given that it is an example which has a ground electronic state which has h (hydrogen atom) properties. Below is a figure reflecting the HOMO and LUMO states of NH4. Attempt to classify these radial functions and explain their relevance to the the description of the nature of these electronic states in NH4. (See: Smith, Jonathan M.; Chupka, William A., "Evidence for a deep Cooper minimum in the 3s-np channel of ND4". Chem. Phys. Lett. 1996, 250, 589-96.) Fig. 2 Radial wavefunctions for NH, HOMO and LUMO orbials aken symametikally berween lydroges pemerand fromGAUSSIAN 2 cakculations. These two wavefunctions appear to be pearty 180t out of phase as would be expected from the experimenal quantam defect differeace of 0.508

Explanation / Answer

A Lewis acid/base reaction is the interaction between a filled molecular orbital and an empty molecular orbital.

HOMO is the highest OCCUPIED molecular orbital and LUMO is the lowest UNOCCUPIED molecular orbital. In an acid / base reaction, the acid is willing to receive electrons from other species, so the energy of the LUMO must be low enough so that electrons can be accepted easily.

On the other hand, the base is willing to give up their electrons, so the energy of the HOMO should be high enough to make the donation easier.

Ammonia has space for 4 electrons in their orbitals.

NH4 curve (HOMO): in this case, the NH4 behaves like a Lewis base capable of donating electrons, so for this to occur easily, there must be sufficient energy (high energy).

NH4 curve (LUMO): in this case, the NH4 behaves like a Lewis acid capable of receiving electrons, so for this to occur easily, there must be low energy, but in this case particulary, the N can't hold another atom of H

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