Showing papers by "Ernest R. Davidson published in 1987"

One‐electron properties of several small molecules using near Hartree–Fock limit basis sets

Abstract: Selected one‐electron properties for eight small molecules (H2O, CO, N2, H2S, NH3, PH3, HCl, and HF) have been computed using extended Gaussian basis sets at the SCF and CI levels. The basis sets and CI methodologies were capable of recovering approximately 86% of the estimated total correlation energy (88% of the valence) and, to the best of our knowledge, yielded the lowest variational energies and closest overall agreement with experimentally determined properties to date. Compared to numerical Hartree–Fock properties the current values are generally within 1%, with the largest deviation being 2.6% for δ at the nucleus. The sensitivity of the computed properties to the basis set composition and type of CI are discussed.

A theoretical investigation of some low-lying singlet states of 1,3-butadiene

Abstract: A theoretical investigation of some low-lying singlet states of 1,3-butadiene,'' J.

ESR and ab initio theoretical studies of the cation radicals 14N+4 and 15N+4: The trapping of ion–neutral reaction products in neon matrices at 4 K

Abstract: The 14N+4 and 15N+4 molecular cation radicals have been generated by the ion–neutral reaction N+2 +N2 and isolated in solid neon matrices at 4 K for detailed ESR (electron spin resonance) investigation. Both photonionization at 16.8 eV and electron bombardment (50 eV) were used in conjunction with the neon matrix trapping technique to produce the N+4 dimer cation. The ESR results clearly show that N+4 is linear and has a 2Σμ ground electronic state. The magnetic parameters in neon are: g∥=2.0016(4) and g⊥=1.9998(2); A∥(14N)=311(1) MHz and A⊥(14N)=264(1) MHz for the central atoms and ‖A∥‖=10.4(5) MHz and ‖A⊥‖=20.4(1) MHz for the outer or terminal 14N atoms. Electronic structure information for N+4 was obtained from the ESR results and compared with ab initio CI calculations. The unpaired electron resides primarily on the inner nitrogen atoms with significant 2pσ and 2s character. Orbital characters obtained from the commonly applied free atom comparison method (FACM) were compared with the results of a Mul...

Laser sputtering generation of B2 for ESR matrix isolation studies: comparison with ab initio CI theoretical calculations

Abstract: The /sup 11/B/sub 2/ molecule has been trapped in neon and argon matrices at 5 +/- 1 K for ESR (electron spin resonance) investigations. Laser sputtering from solid boron was used to generate the B/sub 2/ molecule whose ground electronic state has been established experimentally for the first time to be /sup 3/..sigma../sub g//sup -/. The ESR nuclear hyperfine parameters for B/sub 2/ and B atoms have been compared with the results of ab initio CI theoretical calculations. Good agreement between theory and experiment is found for the dipolar component of the A tensor but not for the small and difficult to calculate isotropic hfs. Reasons that make the Fermi contact term especially difficult to calculate in this particular case are presented. The argon matrix ESR results yield the following magnetic parameters for /sup 11/B/sub 2/ in its ground electronic state: g/sub parallel/ = g/sub perpendicular/ = 2.0015 (4); A/sub parallel/ = +/- 11 (1) MHz and A/sub perpendicular/ = +/- 27.4 (3) MHz for /sup 11/B and the zero field parameter; and the D value is 3633 (3) MHz. As discussed, the most reasonable signs for the A values are A/sub parallel/ 0.more » The neon matrix value of D was found to be 3840 (3) MHz and A/sub perpendicular/ in neon is +/- 26.6 (3) MHz.« less

Ab initio calculation of extended x-ray-absorption fine structure in Br 2

Abstract: A quantitative theory of extended x-ray-absorption fine structure (EXAFS) in diatomic molecules is presented and tested by ab initio calculations in ${\mathrm{Br}}_{2}$. The theory, based on a refinement of conventional EXAFS theory, takes into account (1) an energy-dependent exchange-correlation potential, (2) multielectron excitations, and (3) a single-scattering, spherical-wave expansion. Inelastic processes are included assuming that core-hole excitations and losses in propagation are uncorrelated. We find that a Dirac-Hara exchange potential gives better overall agreement of the EXAFS phase than does the Hedin-Lundqvist potential. The amplitude discrepancy between experiment and single-particle theory can be corrected by adding core-hole lifetime effects, experimental resolution, and multielectron excitations.

Theoretical study of hydridocobalt carbonyls

Abstract: The molecular geometry and electronic structure of hydridocobalt tri- and tetracarbonyls were investigated, by means of ab initio Hartree-Fock calculations in a Gaussian basis set. Two conformations of the tetracarbonyl were found, both having the d/sup 8/, closed-shell electronic configuration. The tricarbonyl complex was found to possess a number of conformations, as well as several low-energy electronic configurations. They examine the geometry, frontier orbitals, and character of chemical bonds of these forms of HCo(CO)/sub 4/ and HCo(CO)/sub 3/, with the aim of determining their relevance to the catalytic activity of the compounds.

A theoretical study of some cobalt carbonyl complexes present in the catalytic cycle of hydroformylation

Abstract: The molecular geometry and electronic structure of formylcobalt tricarbonyl, (eta-ethylene)hydridocobalt tricarbonyl, and ethylcobalt tricarbonyl were investigated by means of ab initio Hartree-Fock and configuration-interaction calculations in a Gaussian basis set. Several stable conformations of each of the complexes were found, and the geometry, frontier orbitals, and the character of chemical bonds of these conformations were examined. Two intramolecular hydrogen migration reactions were investigated, and their energy barriers were found to depend considerably on the choice of the initial and terminal sites of the migrating hydrogen. The effect of electron correlation upon the molecular geometry was examined in some detail in the case of the eta-ethylene complex.

Theoretical Study of Hydridocobalt Carbonyls

Abstract: The molecular geometry and electronic structure of hydridocobalt tri- and tetracarbonyls were investigated, by means of ab initio Hartree-Fock calculations in a Gaussian basis set. Two conformations of the tetracarbonyl were found, both having the d/sup 8/, closed-shell electronic configuration. The tricarbonyl complex was found to possess a number of conformations, as well as several low-energy electronic configurations. They examine the geometry, frontier orbitals, and character of chemical bonds of these forms of HCo(CO)/sub 4/ and HCo(CO)/sub 3/, with the aim of determining their relevance to the catalytic activity of the compounds.