Electronic States Of Ethylene Research Articles

Effective hamiltonians and the quasidegeneracy problem: Calculations on ethylene

We report calculations on the electronic states of ethylene using the canonical transformation cluster expansion formalism to generate an effective valence shell Hamiltonian. The approximate formulas are very sensitive to the partition of one-electron space into core, valence, and excited Orbitals. Consequently, although the formalism in principle should yield the “true” effective valence space Hamiltonian HH for any partition of one-electron space, we find in practice excellent agreement with experiment for theN → T,N → V, and T → V transition energies only when certain potentially catastrophic problems are avoided. Chief among our problems is the “quasidegeneracy” between certain two-particle states. The working formulas for the corrections to the Coulomb interaction resemble those of second-order perturbation theory, with either single-particle or modified energy denominators. If the denominator of just one term becomes very small, the corresponding correction “blows up” leading directly to spurious results for Hv. Besides being extremely cautious about the partition of core, valence, and excited orbitals so as to avoid the problem completely, other suggested solutions range from the inclusion of higher-order terms in the cluster expansion to carrying out the calculation in a localized basis.

Core integrals of 2pπ-electron evaluated from heisenberg's equation of motion

The general formulas for the evaluation of the π–electron core integrals are introduced for homonuclear molecules. The core integrals of the orthogonal and nonorthogonal basis sets α β α and β, and β, are calculated for the specific models. In order to check the validity of the present method, such integrals are applied to the ppp–scf calculations of the electronic states of ethylene, benzene, and naphthalene.

Implications Concerning the Electronic States of Ethylene and Other Olefins from Magnetic Circular Dichroism Measurements of Tetramethylethylene

An investigation of the electronic excited states of tetramethylethylene in the 240−160 nm region has been carried out using synchrotron radiation for magnetic circular dichroism and absorption spectroscopy. These studies show that there are at least six and probably nine electronic transitions in the region once considered to be the sole domain of the π → π*(1B1u) and π → 3s(1B3u) transitions. The most likely assignments for the additional four transitions are π → 3pσ(1B2g), π → 3py(1B1g), π → 3dδ(1B2u), π → 3dδ(1B3u), or σ → σ*. The other three possible electronic transitions are discussed in the paper. These studies also indicate that the positive magnetic circular dichroism bands observed in ethylene are due to an additional electronic transition in the π → π* and π → 3s region and not a vibronically induced part of the π → 3s transition.

The electronic states of ethylene up to 10 eV studied by electron impact spectroscopy and ab initio configuration interaction and iterative natural orbital calculations

The electronic states of ethylene in the range 0–10 eV have been reassessed in the light of new electron scattering data for C 2H 4 and C 2D 4 and ab initio multi-reference configuration interaction and iterative natural orbital calculations with large basis sets. Existing assignments for many low-lying singlet and triplet states are substantiated and a number of new states have been computed. With the exception of the V ( 1B 1u) state which is ππ* and states 2 1B 1g and 2 1B 2g (both σπ*) all of the singlet states in this energy range are of Rydberg character. The role of a resonant intermediate, the 2B 3u anion, in electron scattering from ethylene is confirmed theoretically.

All-valence-electron configuration mixing calculations for the characterization of the 1(π, π *) states of ethylene

Configuration mixing (CM) calculations are reported for the 1(π,π *) and various other electronic states of ethylene. The configuration subspaces considered include all single and double excitations relative to a series of the most important terms in the CM expansion of each state. The lowest-lying 1(π,π *) transition is found to be essentially intra-valence in character with a calculated ∫ value in the 0.25–0.30 range, in good agreement with experiment. Diffuse 3dπ AOs are nevertheless found to be quite important in the representation of the 1(π,π *) state, even after extensive CM: failure to include them in the AO basis results in an energy increase of at least 0.7 eV and substantial overestimation of the corresponding ∫ value by as much as 50%. The vertical 1(π,π *) excitation energy is calculated to be 8.1 eV, while the corresponding 0-0 transition (90° twisted conformation) is predicted in the 6.0–6.2 eV range; very little change in CC bond length is found to occur upon torsion of the CH 2 groups in this state.

Calculation of ???* and ???* transitions in vinylboranes

Calculations are presented of the energies of the ground and excited σ and π electronic states of ethylene and substituted vinylboranes. The Pople-Segal-Santry method was employed throughout. It is concluded that the excited state of lowest energy in ethylene has π→σ * character whilst the lowest energy ultra-violet spectral bands of the latter compounds stem from σ→π * transitions.

Expanded gaussian orbitals and the electronic states of ethylene

Expanded gaussian orbitals and the electronic states of ethylene