A b i n i t i o SCF CI calculations on the ground and π–π* excited states of the pyrrole molecule and its positive ion

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Abstract
Ab initio SCF π‐electron CI calculations are carried out on the ground and lower π–π* excited states of pyrrole and its positive ion. The four singlet states found at 5.9, 6.8, 7.2, and 7.4 eV by experiment are tentatively assigned as the 1B2, 1A1, 1B2, and 1A1 states, respectively. The calculated excitation energies for these four states are 6.0, 6.5, 7.1, and 7.3 eV, respectively. The first excited 1A1 state is a valence type state, whereas the other three states are Rydberg type states. The lowest excited state found at 4.35 eV by experiment is assigned as the 3B2 state, whose calculated excitation energy is 4.27 eV. The three lowest excited states of the positive ion due to π‐electron ionization are also investigated. The calculated ionization potentials are 8.10 (2A2), 8.94 (2B1), and 13.33 eV (2B1). They are in good agreement with experimental values of 8.21, 9.20, and 13.0 eV. The lowest two states are represented by la2→∞ and 2b1 →∞, respectively, whereas the second 2B1 state is a mixture of three configurations (1b1→∞), (2b1 2 →3b1∞), and (1a2 2→3b1∞).

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