Potential energy and dipole moment surfaces for simultaneous torsion and pyramidalization of ethylene in its lowest-lying singlet excited states: A CI study of the sudden polarization effect

Abstract

A b initio CI calculations have been carried out in a double-zeta AO basis for the simultaneous torsion and pyramidalization energy and dipole moment surfaces of the two lowest (V and Z) singlet excited states of ethylene. In nonpyramidalized geometries these two electronic states are found to undergo a potential crossing for a twisting angle of ϑ=82 °, with the Z(1A1) species being the more stable for the perpendicular D2d conformation. The dipole moments of these states are found to increase quite rapidly with pyramidalization for the entire range of twisting angle from ϑ=75 ° to ϑ=90 °, but this effect is found to reach a definite maximum in the neighborhood of the 82 ° crossing region for the unpyramidalized species and it is argued that these two phenomena are in fact closely related to one another. The CI results are found to be strongly dependent on the choice of one-electron basis in the significant portion of key structural regions and it is concluded that the use of natural orbitals optimized for one of the two nearly degenerate singlet states leads to excessively ionic charge distributions. Finally, the minimum-to-minimum energy difference (Te) between the ground and lowest singlet excited state is calculated to be 5.83 eV, suggesting a corresponding T0 value for this transition of 5.6–5.7 eV which is in very good agreement with McDiarmid’s recent experimental determination of this quantity.

Photoinduced dynamics of ethene in the N, V, and Z valence states: A six-dimensional nonadiabatic quantum dynamics investigation

“…As expected, 9,10,14,17,18 the crossing ͑or near degeneracy͒ of the V state with the Z state at near-perpendicular geometry of ethene is reached by a fast spreading of the torsional wave packet on a time scale of the order of 10 fs. A new result of paper I and the present work is the finding that the antisymmetric scissors is the essential coupling mode for the V -Z conical intersection.…”

“…7 and 8 and the references therein. The first accurate calculations of the torsional PE functions of the three valence electronic states N ͑for normal, that is, ground state͒, V ͑for valence͒, and Z ͑for zwitterionic͒ have been performed with the MRD-CI method by Buenker et al 9 and Persico and Bonacić-Koutecký. 10 The so-called sudden-polarization effect, arising from the near degeneracy of V and Z in 90°t wisted ethene, has been investigated in Refs.…”

Abinitio MRD-CI study of NO2. 1. Multi-dimensional potential surfaces for the two lowest 2A′ states

“…On the other hand, a calculation in which C',, symmetry is imposed for r , = r2 gives rise to discontinuity problems, as already mentioned in the previous section and also as encountered by Gillispie et al in their NO' study (2). The problem of the variation of CI results on the choice of the one-electron basis for close-lying electronic states has been previously discussed in a CI study of the sudden polarization effect (23,24). Figures 2-4 show that the crossing seam in the 'A' surfaces is located near 107" for all chosen distances, but that the energy of the crossing goes up considerably when going to smaller bond distances.…”

Solvent Induced Charge Separation in the Excited States of Symmetrical Ethylene: A Direct Reaction Field Study

“…Several configuration interaction (CI) studies on ethylene have shown that at (near) perpendicular geometries three important singlet states arise: the N state, which is the (CR) ground state at this geometry, and the ionic Z and V states, which become degenerate at a central bond twist angle of about 80°. 9,12 In the vicinity of this degeneracy, lowering of the nuclear symmetry by pyramidalizing one of the carbon centers leads to the formation of considerable dipole moments in the Z and V states of ethylene.…”

“…A large number of both experimental 27,28,34,38,42,43,48,51,52,56 and theoretical 3,9,12,15,23,[58][59][60] studies have been performed in an attempt to gain both experimental evidence and additional information about the driving forces governing this symmetry breaking, which is often referred to as sudden polarization, 4 especially in the condensed phase.…”