William C. Swope

Diatomic sulfur: Low lying bound molecular electronic states of S2

We present here the results of self‐consistent field (SCF) and configuration interaction (CI) type calculations on thirteen low‐lying electronic states of diatomic sulfur. The basis set was one of double zeta quality augmented with polarization functions. The CI space for each electronic state consisted of all configurations constructed from single and double excitations of electrons from the valence orbitals of the Hartree–Fock configuration. There are several significant findings of this study. First, we report the discovery of a previously unobserved and bound 1Πu state which lies approximately 37 000 cm−1 above the ground state. This state dissociates to two ground state sulfur atoms. Second, we provide new predictions of excitation energies and properties for the three states e1Πg, c1Σ−u, and B′3Πu. These states were suspected or known to be bound, but experimentally determined properties were uncertain. Finally, we find that systematic application of a formula of Davidson, which estimates the contri...

The H3+ potential surface

An accurate potential surface of 68 grid points for the H3+ system is given. The surface was calculated at the level of a full configuration expansion using a large basis set of 63 contracted Gaussian functions. This surface should be suitable for extremely accurate predictions of the vibration–rotation spectrum of H3+.

The uncoupled symmetric stretching frequency of H3

The a b i n i t i o D 3h potential energy surface for H3 + has been calculated using the method of self‐consistent electron pairs (SCEP). The symmetric stretching frequency is estimated to be 3347.3±0.5 cm−1 from these calculations.(AIP)

Sulfur oxide: Low‐lying bound molecular electronic states of SO

We present here the results of self‐consistent field (SCF) and configuration interaction (CI) theoretical studies of seven low‐lying electronic states of sulfur oxide. The basis set was of double zeta quality augmented with polarization functions. The CI space for each electronic state consisted of all configurations constructed from single and double substitutions of electrons from the valence orbitals of the Hartree–Fock reference occupation. Spectroscopic constants as well as dipole moments for each electronic state were predicted both at the SCF and CI levels of theory. Of particular significance is the prediction of excitation energies and properties for three low‐lying states for which experimental information is either unavailable or only very recently available. These states are the c1Σ− state (Te=28 100±300 cm−1), the A′ 3Δ state (29 200±300 cm−1) and the A″ 3Σ+ state (30 200±300 cm−1).

Model studies of π-bonded organometallic systems Mn-C2H2 and Mn-C2H4

An improved understanding of the structural and energetic aspects of transition metal-carbon bonds is essential to progress in surface chemistry, catalysis, and organometallic chemistry. As a possible route to this goal, ab initio electronic structure theory has been applied to two very simple systems, Mn-C2H2 and Mn-C2H4. Single configuration self-consistent-field theory was used in conjunction with a better than double zeta basis set of contracted gaussian functions. For the manganese-acetylene system, potential energy curves were predicted for electronic states arising from Mn+(4s3d5) and Mn(4s23d5, 4s4p3d5, and 4s3d6) interacting with the 1Σ g + ground state of C2H2. For the first three dissociation limits, the present results are consistent with those based on the earlier studied Be-C2H2 model system. The latter model assumes that metal 3d orbitals play a relatively passive role in the bonding. The 4s3d6 dissociation limit has no counterpart for the Be-C2H2 system, and the predicted potential energy ...

A genealogical electronic coupling procedure incorporating the Hartree–Fock interacting space and suitable for degenerate point groups. Application to excited states of BH3

The use of Clebsch–Gordan‐type coupling coefficients for finite point groups is applied to the problem of constructing symmetrized N‐electron wave functions (configurations) for use by the Hartree–Fock SCF and CI methods of determining electronic wave functions for molecular systems. The configurations are eigenfunctions of electronic spin operators, and transform according to a particular irreducible representation of the relevant group of spatial operations which leave the Born–Oppenheimer Hamiltonian invariant. The method proposed for constructing the configurations involves a genealogical coupling procedure. It is particularly useful for studies of molecules which belong to a group which has multiply degenerate irreducible representations. The advantage of the method is that it results in configurations which are real linear combinations of determinants of real symmetry orbitals. This procedure for constructing configurations also allows for the identification of configurations which have no matrix el...

A harmonic oscillator model for the magnetic properties of a closed-shell system

It is shown that the magnetic shielding tensor of a nucleus in the presence of a charged anisotropic harmonic oscillator may be reduced to quadrature, hence providing an exactly solvable model for the effect of Van Vleck paramagnetism on the chemical shift. Two cases are examined in detail, oblate and prolate ellipsoids of revolution. In addition the electric polarizability, magnetic susceptibility and chemical shift tensors of the H2 molecule are examined in terms of the theory.