P. A. G. O'Hare

Molecular Orbital Investigation of CF and SiF and Their Positive and Negative Ions

Accurate Hartree–Fock self‐consistent‐field wavefunctions have been computed for CF, CF+, and CF− at several internuclear separations by the Roothaan expansion method. Similar wavefunctions were also computed for SiF, SiF+, and SiF− at the parent molecule internuclear separation. A Dunham analysis of the energy curves for the three CF species yielded values for the spectroscopic constants. Other properties deduced in the present research include the first and second ionization potentials, electron affinities, and dipole and quadrupole moments for CF and SiF. The dipole moment calculated for CF is consistent with a charge distribution corresponding to a C−–F+ configuration. In addition, the correlation energies of a number of light‐element diatomic fluorides have been deduced from literature data and from results given in the present paper. It appears that the correlation energy increment between adjacent diatomic fluorides is virtually constant for molecules of the first row of the periodic table.

Oxygen Monofluoride (OF, 2π): Hartree–Fock Wavefunction, Binding Energy, Ionization Potential, Electron Affinity, Dipole and Quadrupole Moments, and Spectroscopic Constants. A Comparison of Theoretical and Experimental Results

Self‐consistent‐field wavefunctions near the Hartree–Fock limit have been calculated by the Roothaan expansion method for OF(2π) at several internuclear separations; the total energy at the Hartree–Fock minimum (1.321 A) was found to be − 174.19502 hartree. Based on the assumption that the correlation energy was approximately the same as for O2−, and also by interpolating the correlation energy of OF across the CF, NF, OF, and F2 sequence, the binding energy D(OF) was deduced to be 3.0+0.3−0.8 eV. A Dunham analysis of the potential‐energy curve gave values for the various spectroscopic constants. In addition, the ionization potential and electron affinity for the vertical processes, and the dipole and quadrupole moments of OF+(3Σ), OF(2π), and OF−(1Σ) were also calculated.

Thermochemical and Theoretical Investigations of the Sodium‐Oxygen System. II. Properties of NaO and Its Ions from Hartree‐Fock Molecular Orbital Studies

Accurate Hartree‐Fock wavefunctions, computed by the method of Roothaan, are reported for the 2II and 2Σ states of NaO, for the 3Σ state of NaO+, and for the 3II, 3Σ, and 1Σ states of NaO−. Spectroscopic constants and dipole and quadrupole moments have also been calculated for each of the molecules and ions. Several properties of the Na–O species have been deduced. These properties include the vertical and adiabatic ionization potentials (7.7 and 7.4 eV), electron affinity (1.1 eV), dissociation enthalpy (2.7 eV), several thermodynamic functions for NaO, and the 3Π →1Σ (1.7 eV) and 3Π →3Σ (0.2 eV) excitation energies for the NaO− system. Thermodynamic data for selected reactions involving NaO and NaO+ are given, together with a brief discussion of the bond enthalpies in NaO2 and NaO2+.

Quantum‐Chemical Study of Some Pnicogen Monofluorides

A quantum‐chemical investigation of the nitrogen–fluorine and phosphorus–fluorine diatomic systems is described. Molecular self‐consistent‐field wavefunctions near the Hartree–Fock limit were computed via the Roothaan expansion method for the X 3Σ− (ground), a 1Δ, and b 1Σ+ states of NF and for the 2Π states of NF+ and NF−. Similar wavefunctions were computed for the 3Σ− ground state of PF and for PF+(2Π) and PF−(2Π). For the neutral molecules, the experimental bond lengths were used; for the charged species, the internuclear separations of the parent (3Σ) molecules were used. In addition, a wavefunction was also obtained for PF+(2Π) at its experimental internuclear separation. Values derived for the binding and ionization energies through the use of semiempirical correlation energies are in excellent agreement with experimental data; the uncorrelated excitation energies, as expected, are somewhat different than the experimental results. The electron affinities deduced from the wavefunctions indicate that...

Dissociation Energies, Enthalpies of Formation, Ionization Potentials, and Dipole Moments of NS and NS+

A dissociation energy of 4.8 ± 0.25 eV at 0°K has been deduced for NS(2Π) from spectroscopic data in the literature; the corresponding value for ΔHf0°(NS) is 2.91 ± 0.26 eV. Recent experimental results for ΔHf°(NSF) from this Laboratory indicate ΔHf0°(NS+, 1Σ+) = 12.76 ± 0.10 eV, from which the ionization potential of NS, 9.85 ± 0.28 eV, is obtained. Hartree–Fock–Roothaan ab initio calculations for NS and NS+ yielded, respectively, first ionization potentials of 9.75 and 24.3 eV, dipole moments of 1.732 and 3.893 D, and, for D0° (NS), an approximate value of 5.2 eV.

Properties of the monofluorides of nitrogen, silicon, phosphorus, and sulfur from a molecular orbital study

Self‐consistent‐field wavefunctions near the Hartree‐Fock limit have been computed for the 3Σ states of NF and PF, and for the 2Π states of SiF and SF. Based on a Dunham analysis of the computed total energies, results have been derived for the equilibrium bond lengths and spectroscopic constants. Values of 830 ± 20, 4.7, and 0.0042 cm−1 are predicted for the hitherto undetermined ωe, ωexe, and αe of SF. Computed ionization potentials are in excellent agreement with experiment. Electron affinities of −0.1, 1.1, 1.1, and 1.7 eV are predicted for NF, SiF, PF, and SF, respectively. The dissociation enthalpy D0° of PF is estimated to be 4.65 ± 0.2 eV, and values of 0.25, 0.5, and 0.6 D are suggested for the dipole moments of NF, SiF, and PF, respectively. Dissociation enthalpies of the positive and negative ions have also been calculated. A previously calculated re(OF) has been revised to 1.34 A.

Dissociation Energy, Ionization Potential, Electron Affinity, Dipole and Quadrupole Moments of Chlorine Monoxide (ClO, 2Π) from Ab Initio Molecular Orbital Calculations

Molecular self‐consistent‐field wavefunctions near the Hartree–Fock limit have been computed by the Roothaan expansion method for ClO(2Π), ClO+(3Σ), and ClO−(1Σ) at an internuclear separation of 1.570 A. Combination of the computed total energies with estimates for the molecular extra correlation energies yielded values of < 2.9, 2.2 ± 0.5, and 11.2 ± 0.4 eV for the binding energy, vertical electron affinity, and vertical ionization potential, respectively, of ClO. The above results, and the computed dipole moment, 0.81 ± 0.16 D, are in satisfactory agreement with experimental data. In addition to the above properties, the dipole and quadrupole moments have been calculated for ClO+ and ClO−.

Hartree–Fock Wavefunctions and Computed Properties for the Ground (2π) States of SF and SeF and Their Positive and Negative Ions. A Comparison of the Theoretical Results with Experiment

Self‐consistent‐field wavefunctions, near the Hartree–Fock limit, have been computed by the Roothaan expansion method for SF(2π) and SeF(2π) at the experimental internuclear separations. The results from the present investigation, coupled with our previous calculations on OF, show that the Hartree–Fock binding energies of OF, SF, and SeF vary nonmonotonically, in harmony with the experimental dissociation enthalpies. Other properties reported herein for SF and SeF include the vertical ionization potentials and vertical electron affinities, and the dipole and quadrupole moments for the neutral and charged species. The computed ionization potential for SF suggests that the experimental appearance potentials for SF+ are too large by approximately 2 eV. Thermodynamic calculations based on the electron affinities predict substantial stabilities for SF− and SeF− at moderate temperatures.

Thermochemical and Theoretical Investigations of the Sodium‐Oxygen System. I. The Standard Enthalpy of Formation of Sodium Oxide (Na2O)

Calorimetric measurements of the enthalpy of hydrolysis of pure sodium oxide (Na2O) are described. Based on the enthalpy of reaction, the standard enthalpy of formation at 298.15°K, Δ Hf298o(Na2O), was calculated to be −414.82± 0.28 kJ mole−1 (−99.14± 0.07 kcal mole−1). The enthalpy of reaction reported in the present study is significantly more exothermic than that determined by previous investigators. This discrepancy is attributed to the probable presence of hydroxide, carbonate, or other contaminants in the earlier sodium oxide samples.

Uranium Diboride: Preparation, Enthalpy of Formation at 298.15°K, Heat Capacity from 1° to 350°K, and Some Derived Thermodynamic Properties

A sample of uranium diboride was prepared and characterized as UB1.979±0.006 with 0.06 ± 0.03 wt % of identified impurities. The standard enthalpy of combustion in fluorine was determined to be − 1021.2 ± 1.1 kcal mole−1. The heat capacity was measured from 0.84° to 350°K. At 298.15°K the heat capacity CP°, entropy S°, and enthalpy increment H° − H°0 are 13.23 ± 0.03 cal K−1·mole−1, 13.17 ± 0.03 cal °K−1·mole−, and 2108 ± 4 cal mole−1, respectively. The following values were obtained for the standard enthalpy, entropy, and Gibbs energy of formation of UB2 at 298.15°K: ΔHf° = − 39.3 ± 4.0 kcal mole−1, ΔSf° = − 1.54 ± 0.05 cal °K−1·mole−, and ΔGf° = − 38.8 ± 4.0 kcal mole−1. These agree within experimental error with values calculated from high‐temperature effusion measurements. The heat‐capacity results below 4.2°K follow the equation CP = (9.40 ± 0.01)T + (3.18 ± 0.14) × 10−2T3mJ °K−1·mole−1. The relatively high value for the coefficient of the linear term indicates that uranium diboride is a good electri...