Abstract
Ab initio SCF and CI treatments of the ground state and n → π* and π → π* excited states of pyrazine, C4H4N2, are reported for the molecule in its ground state equilibrium geometry. In the case of n → π* transitions, the two symmetry combinations of nitrogen lone pair orbitals n1 and n2 are found to correspond to the description n+ ≈ n1 + n2 + λσ and n− ≈ n1 − n2 in which the n+ orbital has the higher orbital energy and is significantly more delocalized than n− by interaction with the pyrazine ring sigma system. This result leads to a significant splitting at the CI level of description of 1.4 eV between the B3u and B2g excited states which are derived from the orbital promotions n+ → π* and n− → π*, respectively. Calculated transition energies to the lowest n → π* excited states B3u3 and B3u1 of 3.56 and 4.22 eV, respectively, are in good agreement with experimental values. A low-lying B1u3(π → π*) state for which there exists indirect experimental evidence is found to occur between the B3u3 and B3u1 states. Also, an allowed transition to the B2u1(π → π*) state is calculated at 5.29 eV, slightly above the observed range of absorption. Numerous other excited states are calculated, but of these only the B1u1(π → π*) and B2u1(π → π*) states can be identified with observed transitions and in these cases the calculated transition energies are too high by approximately 2.5 eV.
References
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Dates
| Type | When |
|---|---|
| Created | 21 years, 6 months ago (Feb. 6, 2004, 3:15 p.m.) |
| Deposited | 1 year, 6 months ago (Feb. 9, 2024, 3:22 a.m.) |
| Indexed | 1 year, 4 months ago (April 15, 2024, 4:28 p.m.) |
| Issued | 54 years, 3 months ago (May 1, 1971) |
| Published | 54 years, 3 months ago (May 1, 1971) |
| Published Print | 54 years, 3 months ago (May 1, 1971) |
@article{Hackmeyer_1971, title={Configuration Interaction Studies of Ground and Excited States of Polyatomic Molecules II. The Electronic States and Spectrum of Pyrazine}, volume={54}, ISSN={1089-7690}, url={http://dx.doi.org/10.1063/1.1675423}, DOI={10.1063/1.1675423}, number={9}, journal={The Journal of Chemical Physics}, publisher={AIP Publishing}, author={Hackmeyer, Melvyn and Whitten, J. L.}, year={1971}, month=may, pages={3739–3750} }