Correct option is A
The molecular orbitals (MOs) of a water molecule arise from the interaction of the oxygen atom's atomic orbitals with those of the hydrogen atoms. The geometry and symmetry of these molecular orbitals influence their energy levels and the distribution of electrons in the molecule.
Photoelectron Spectrum and Symmetry:
Photoelectron Spectrum: The photoelectron spectrum provides information about the energy levels of molecular orbitals by measuring the energy required to remove electrons from them. This allows the determination of different MO energies, including lone-pair orbitals.1
Lone-Pair Orbitals: In water, the lone pairs on oxygen are found in two different molecular orbitals, and these have distinct energies due to their different spatial orientations and interactions with other orbitals.
Symmetry of Bond Orbitals: The bond orbitals (O-H bonds) in water have specific symmetry properties. Symmetry labels like a1 are assigned based on how the orbitals transform under molecular symmetry operations.
Statement A: The photoelectron spectrum shows two MOs with lone pairs having different energies because one lone-pair MO is more localized on the oxygen atom (with little interaction with hydrogen), while the other interacts more strongly with the molecular framework, resulting in different energy levels.
Statement C: The HOMO is mainly an oxygen p orbital because oxygen is more electronegative than hydrogen.
Additional Knowledge
Statement B: The O-H bond orbitals do not have a1 symmetry; they correspond to other modes of bonding.
Statement D: Increasing the bond angle typically stabilizes the HOMO instead of destabilizing it.
