?The highest occupied molecular orbital of a molecule is abbreviated as the HOMO. The

Chapter 9, Problem 9.104

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The highest occupied molecular orbital of a molecule is abbreviated as the HOMO. The lowest unoccupied molecular orbital in a molecule is called the LUMO. Experimentally, one can measure the difference in energy between the HOMO and LUMO by taking the electronic absorption (UV-visible) spectrum of the molecule. Peaks in the electronic absorption spectrum can be labeled as \(\pi_{2 p}-\pi_{2 p^{*}}\), \(\sigma_{2 s}-\sigma_{2 s}{ }^{*}\), and so on, corresponding to electrons being promoted from one orbital to another. The HOMO-LUMO transition corresponds to molecules going from their ground state to their first excited state.

(a) Write out the molecular orbital valence electron configurations for the ground state and first excited state for N2.

(b) Is N2 paramagnetic or diamagnetic in its first excited state?

(c) The electronic absorption spectrum of the N2 molecule has the lowest energy peak at 170 nm. To what orbital transition does this correspond?

(d) Calculate the energy of the HOMO-LUMO transition in part (a) in terms of kJ/mol.

(e) Is the N 一 N bond in the first excited state stronger or weaker compared to that in the ground state?

Text Transcription:

pi_2p-pi_2p^*

sigma_2s-sigma_2s^*