Bernard J. Ransil

Studies in Molecular Structure. IV. Potential Curve for the Interaction of Two Helium Atoms in Single‐Configuration LCAO MO SCF Approximation

Single‐configuration LCAO MO SCF wave functions and corresponding total energies were calculated for two ground‐state He atoms interacting over an extensive range (0.4 to 12.0 A). Comparison with available experimental data is made; remarkably good agreement is obtained for distances greater than 1.5 A. For the first time, it is believed, an a priori account is given of both the van der Waals minimum and the repulsion region with a wave function of sufficient flexibility to deal with both. The details of repulsion and of bonding in the van der Waals region are analyzed in terms of atomic and overlap populations.

Studies in Molecular Structure. VI. Potential Curve for the Interaction of Two Hydrogen Atoms in the LCAO MO SCF Approximation

The LCAO MO SCF method, both in the single‐configuration and a limited configuration interaction approximation, has been utilized to evaluate the potential curve of the ground state of H2; wave functions and total molecular energies are presented for a wide range of the internuclear distance (1.0 a.u. ≤R≤18.0 a.u.). These solutions were then used to construct potential curves for the ground states of the molecular ions H2+ and H2— and for the lower‐lying excited states of the neutral molecule. Results of vibration‐rotation analyses for the stable states are presented. The results for a population analysis of the single‐configuration ground‐state function over the whole range of R are given, and compared to similar results for He2.

Studies in Molecular Structure. V. Computed Spectroscopic Constants for Selected Diatomic Molecules of the First Row

Limited LCAO MO functions were computed for several diatomic molecules at four different values of the internuclear distance near Re, and the corresponding total energies fitted to a third degree polynomial in R. Spectroscopic constants ωe, ωexe, Be, αe, Re, ke were derived from the resulting potential curve and compared to observed values. The good agreement obtained in most cases suggests a valuable application of the self‐consistent field function. In addition calculations were made for a few more values of the internuclear distance providing a potential curve over a reasonably broad range around Re.

Studies in Molecular Structure. VII. Limited Configuration Interaction for Selected First‐Row Diatomics

Calculations on selected first‐row diatomic molecules using a limited configuration interaction with minimal LCAO MO SCF wave functions are described. Molecular energies, dipole moments, and population analyses are tabulated and discussed. These results provide an extensive foundation for a tentative evaluation of the value of limited configuration interaction for LiH, BH, NH (d1Σ+), HF, Li2, C2, N2, F2, LiF, CO, and BF within the limits of the approximations used.

Toward a Charge‐Density Analysis of the Chemical Bond; The Charge‐Density Bond Model

Total‐charge‐density diagrams (ρ diagrams) are presented for the ground states of Li2, N2, F2, HF, and LiF in BMMO (best minimal molecular‐orbital) and accurate SCF (self‐consistent‐field) approximations. On the basis of contour geometry the ρ diagrams are partitioned into regions of localized and delocalized charge density for which approximate average electron populations, called PL and PD, respectively, are computed. The PL are computed as a function of contour value and contour radius and provide a quantitative measure of the degree of charge transfer in the neighborhood of the nuclei attributable to molecule formation. Criteria for binding, nonbinding, and antibinding, following Berlins treatment of the Hellmann—Feynman electrostatic theorem, are discussed. A positive correlation between the binding energy De and the ratio PD/PL is noted.An alternate approach to interpreting the ρ diagram is introduced, in which charge‐density‐difference diagrams (Δρ diagrams) are interpreted as bond maps, i.e., dia...

Studies in Molecular Structure. VIII. He2++ in the Single‐ and Many‐Configuration LCAO MO SCF Approximation

Single‐ and many‐configuration wave functions and their corresponding molecular energies are reported for the diatomic molecular ion He2++ in the LCAO MO SCF approximation for a wide range of internuclear distances. A potential curve displaying a minimum at 0.71 A and a maximum at about 1.11 A is obtained with ωe=3295 cm—1 and De=1.21 eV. Comparison with potential curves and correlation energies computed by the more accurate methods of Kolos, Roothaan, Weiss, Yoshimine, and McLean are made. The results are discussed with reference to stability and occurrence of the ion. Correlation energy is computed as a function of internuclear distance and compared with the isoelectronic analog H2.

Studies in Molecular Structure. III. Populations Analyses for Selected First‐Row Diatomic Molecules

Electronic population analyses for selected diatomic molecules of the first row of the periodic table are tabulated. The tentative value of population analyses in relation to accuracy of approximation is discussed briefly.

Magnetic Interaction of H3

The results of an LCAO—MO—SCF—CI calculation of the 2Σu ground state of linear H3 are presented and the wave functions obtained from this calculation are used to calculate the general features of the electron spin resonance spectrum. The calculation is carried through for the Fermi contact interaction, which is the principal interaction between the proton and electron spins. It is found that the off‐diagonal elements of the hyperfine interaction matrix may not be neglected in that they split degenerate levels. The predicted spectrum, however, does not agree with the observed electron spin resonance spectrum of discharged hydrogen deposited at liquid helium temperatures. In addition the expected electron spin resonance spectrum of H2+ has been calculated from the exact wave function.