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Various geometric isomers of C 5 have been studied via ab initio calculations in order to determine the equilibrium structure. Hartree-Fock calculations were performed using both double-zeta and double-zeta plus polarization basis sets. Electron correlation was included via second-order Mriller-Plesset perturbation theory. It is concluded that C 5 is linear, in agreement with recent laser vaporization studies.

The geometric and electronic structures and the total and binding (chemisorption) energies of linear Cn (n=6−10) and HCnH (n=2−10) molecules have been predicted via RHF ab initio calculations. For Cn clusters the bonding structures are predicted to be cumulene type, with n-even clusters having triplet ground states and n-odd species having singlet ground states. For HCnH molecules, the n-even species are predicted to have singlet ground states with polyyne-type bonding while the n-odd molecules are predicted to have triplet ground states with intermediate cumulene—polyyne-type bonding.

Restricted Hartree-Fock calculations have been carried out on linear LiCnLi (n=2–8) molecules. Ground state electronic structures, total energies, binding energies, and optimized geometries are reported. The possibility of basis set superposition error is examined. Extensive bond pattern change is found by comparison with linear Cn molecules.

Total energies, bond lengths, charge distributions, electronic configurations, and cohesive energies are calculated for linear Cn clusters, n = 2–6. The calculations are done at the single determinant Hartree-Fock level using both double-zeta and double-zeta plus polarization basis sets.

Configuration interaction of low‐lying electronic states is used to investigate the molecular correlation energy as a function of bond angle. Qualitative aspects of the problem are discussed using the molecular‐orbital diagrams of Walsh and Mulliken. Results of configuration‐interaction calculations of BeH2 and NO2+ are reported. The possibility of double minima in the potential surfaces for AB2 molecules is considered.

The geometry and binding energy of the H5+ molecular ion have been examined by two different ab initio quantum mechanical variational methods. In the first a CI wavefunction was made from the 10 covalent valence‐bond structures which could be constructed from 1s orbitals at the nuclei, each 1s orbital being represented by a five‐term Gaussian expansion and having a variable scale factor. For geometries identical or similar to the D2d geometry previously predicted from analogous calculations with cruder basis sets, we found no stability with respect to H3++H2. Other geometries were examined, especially those arising naturally from the approach of H3+ and H2; however, binding was never greater than a tiny 0.6 kcal/mole. We thus concluded that the method had failed adequately to describe H5+, as it had for H3+, and that it is probably unreliable for studying ions with small binding energies. The second method used the SCF MO model with a flexible basis set to account for distortion and polarization. This gav...

A new technique for the determination of atomic valence states and their energies has been developed and applied to the water molecule and hydroxyl radical. This method is applicable to valence-bond studies involving a large number of resonance structures rather than simply a one structure perfect pairing approach. The original basis of resonance structures is transformed into a basis of approximate composite functions which are orthogonal and non-interacting for the separated atoms. The equilibrium molecular eigenfunction is analyzed in terms of the composite functions by means of structure projections. A description of the valence states and the promotional energies of each of the component atoms in H2O and OH is obtained.

The electronic structure of NO2+ and NO2− has been investigated as a function of angle by means of ab initio MO LCAO SCF wavefunctions. Atomic orbitals used in the basis set are close to free‐atom Hartree–Fock solutions. Several excited states, in addition to the ground states, have been obtained for the two ions. Total energies, population analyses, and one‐electron orbital energies vs angle (Walsh diagrams) have been computed to aid interpretation of the wavefunctions. It turns out that the dramatic change in geometry from NO2+ (linear) to NO2− (bent, 115.4°) can be understood by the occupancy and shape of a single orbital, the 6a1 in NO2−. Our results contribute to the establishment of a firm mathematical and numerical foundation of Walsh's rules and diagrams. The present calculations also serve to substantiate and extend previous wavefunctions for these important chemical species.

Recent experiments involving laser vaporization of graphite, followed by supersonic expansion, 1–4 have rekindled interest in the structures of small carbon clusters. While theoretical calculations have firmly established the structure(s) of 04, 5–8 relatively little theoretical work has thusfar been reported for C5 and C5, most such studies being small model calculations on diamond and graphite. There has been, however, a MINDO/2 geometry search on small carbon clusters which included C5 and C6 9. in that work C5 was found to be trigonal bipyramidal, and C5 was found to be a distorted octahedron of C2V symmetry. The available experimental data, from matrix isolation studies, indicate that C5 and C5 are linear.10–11

Describes a convenient procedure, the Odd-Even Rule, for predicting the allowedness or forbiddenness of ground-state, pericyclic reactions.