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On the Correlation between Ionization Potentials and Excitation Energies, part III: Pyrazine
Author(s) -
Haselbach Edwin,
Lanyiova Zuzanna,
Rossi Michel
Publication year - 1973
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19730560826
Subject(s) - chemistry , excitation , ionization , pyrazine , ionization energy , atomic physics , x ray photoelectron spectroscopy , spectroscopy , binding energy , ion , stereochemistry , nuclear magnetic resonance , physics , quantum mechanics , organic chemistry
A recently suggested scheme for relating ionisation potentials ( IP ) to excitation energies ( E ) has been applied to pyrazine and 2,6‐dimethylpyrazine. The results indicate that in these systems the energy gap (Δ E ) between the two lowest lying 1 n ,π*‐states is significantly smaller than that (Δ IP ) between the corresponding 2 n ‐states of the parent radical cations. The values estimated for Δ E on the basis of Δ IP , measurable by photoelectron spectroscopy, disagree with those calculated theoretically but seem to be supported by the experimental evidence available. Since Δ E = Δ IP would normally be expected, the relationship Δ E < Δ IP actually present in these systems is discussed and related to the different shape of the n ‐MO's involved in the ionization and excitation processes.