Hubert W. Joy

Mass‐Spectrometric and Theoretical Evidence for NH4 and H3O

The unusual chemical species H3O and NH4 have been studied using both experimental and theoretical methods. Experimentally the species were investigated by means of a mass spectrometer equipped with two different reactors designed to produce reactive species. The NH4 was produced by surface chemistry techniques, whereas H3O was produced by irradiating water vapor with ionizing electrons. A study of the ionization potential of NH4 by surface ionization techniques gave a value of 5.9 eV. The ionization potential of H3O was measured by conventional techniques and a value of 10.9 eV was obtained. In the theoretical investigation, the physical parameters are given including s‐, p‐, and d‐type orbitals for H3O and s‐, p‐, and f‐type orbitals for NH4. The calculations for NH4 predict a tetrahedral structure with internuclear distances of about 1.06 A and they predict a planar H3O molecule with bond distances about 1.03 A. The ionization potentials of H3O and NH4 were estimated to 3.9 and 3.0 eV.

On One‐Center Expansions in H2+

An analysis of several alternative forms of one‐center expansion of the ground‐state H2+ wavefunction is presented in the context of a comparison of three recent one‐center expansions, together with new numerical results. A 14‐term one‐center function having energy −1.10121 hartree is given.

Convergence in One‐Center Expansions. H2+

Inter‐ and intrashell convergence in a one‐center expansion of H2+ for the 1sσg and 2pσu states is examined and convergence laws deduced.

CONSTANT ENERGY AND MINIMUM ENERGY ORTHOGONALIZATION

The problem of orthogonalizing a set of orbitals is considered, noting that the energy calculated for a determinantal wavefunction is often changed by such a procedure. Rules are given for finding whether a particular determinantal wavefunction will, in fact, yield different results on orthogonalization of its basis set. A new orthogonalization procedure, minimum energy orthogonalization, is illustrated, and some of its possible uses are examined.

Valence states of carbon in π-electron systems

Changes in atomic orbitals (AO) brought about by changes in molecular wavefunctions are studied by minimizing the energy of carbon in atomic valence states appropriate for ions and excited states of alternant hydrocarbons. It is found that positive-ion and triplet-state 2pπ AOs are more contracted than in alternant hydrocarbon ground states. Negative-ion and excited-singlet 2pπ AOs are more expanded than in the ground states. These AO changes may be negligible for large molecules but are increasingly important for molecules smaller than naphthalene.

Computations to Evaluate Dewar's Split P‐Orbital (SPO) Method

The split p‐orbital (SPO) wavefunction derived from the single determinant | 2pz2pz | corresponding to the singlet state in which a single 2pz orbital is doubly occupied, correlates the electronic motion so that the electrons always occupy opposite lobes of the 2pz orbital. This SPO singlet wavefunction may be written as 2—½{— | 2pz2pz | + | | 2pz | | 2pz | |} and is the lowest‐energy linear combination of this pair of two‐electron determinants. In this two‐electron context, the triplet function | 2pz | 2pz | | is degenerate with the SPO singlet. In order to test the persistence of this qualitative picture when occupied sigma core orbitals are explicitly included, we have performed analogous rigorous computations on the 1s22s22pz2 nonstationary state of carbon, using corresponding determinants | 1s1s2s*2s*2pz2pz | and | 1s1s2s*2s* | 2pz | | 2pz | |, which include occupied 1s and 2s core orbitals. The lowest‐energy singlet linear combination is found to be almost entirely composed of the first det...

S Limit in Helium. Movement of a System on an Energy Surface in Parameter Space

As part of a variational examination of angular correlation in electronic systems, a careful examination of the movement of a system on an energy surface in parameter space has been made. The results indicate that the surface is highly convoluted, and that minimization techniques must take explicit account of this. An eight‐term result close to the S limit in helium is given.

Ionization Potentials and Autoionization Levels of Methyl, Ethyl, n‐Propyl, and n‐Butyl Free Radicals by an Energy‐Calibrated Molecular Orbital Method

Ionization potentials and possible autoionization levels of the methyl, ethyl, n‐propyl, and n‐butyl free radicals have been calculated with an energy‐calibrated molecular orbital method. Molecular orbitals were constructed as a linear combination of 1s hydrogen and 2p carbon atomic orbitals. Autoionization levels were calculated from molecular orbitals constructed to include autoionizing levels of the carbon atom (2p3, 1D, etc.). Two different models of the free radicals were formulated for the calculations, a simple planar model in which the interaction of the atomic orbitals was restricted to adjacent atoms, and a more complicated group model in which the interactions of the orbitals were much less restricted. Calculations in both models were based upon the assumption that the ionization processes are principally controlled by the unpaired carbon 2p electron. Calculated and experimental values are in reasonable agreement over the energy range of the experimental data. The lowest ionization potential of...

Radial Correlation in Helium

Preliminary results on the energy limit reached for the ground state of helium with functions including radial coordinates only are reported. The results led to speculation on the use of angular ( THETA /sub ij/) rather than interelectronic (r/sub ij/),