?You are now ready to understand more deeply the features of photoelectron spectra

Chapter 11, Problem P11F.5

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You are now ready to understand more deeply the features of photoelectron spectra (Topic 9B). Figure 11.3 shows the photoelectron spectrum of HBr. Disregarding for now the fine structure, the HBr lines fall into two main groups. The least tightly bound electrons (with the lowest ionization energies and hence highest kinetic energies when ejected) are those in the lone pairs of the Br atom. The next ionization energy lies at 15.2 eV, and corresponds to the removal of an electron from the HBr \(\sigma\) bond. (a) The spectrum shows that ejection of a σ electron is accompanied by a lot of vibrational excitation. Use the Franck–Condon principle to account for this observation. (b) Go on to explain why the lack of much vibrational structure in the other band is consistent with the nonbonding role of the \(\operatorname{Br} 4 p_{x}\) and \(\operatorname{Br} 4 p_{y}\) lone-pair electrons.

Text Transcription:

sigma

Br4p_x

Br4p_y