Nicholas W. Winter

Configuration interaction studies of the excited states of water

We report the results of extensive configuration interaction studies on 16 excited states of water. These states can be accurately described as corresponding to excitation from one of the highest two molecular orbitals (1b_1 or 3a_1) of the ground state into either the 3s or one of the three 3p Rydberg orbitals. The results provide the most accurate and consistent treatment of these states to date (within 0.1 eV for all known transitions) and form a reliable basis for the assignment of the photon and electron impact spectra of H_2O.

Theoretical assignments of the low-lying electronic states of carbon dioxide

Abstract Extensive configuration interaction calculations (1000 to 1500 determinants) have been carried out for the six low-lying valence states of carbon dioxide in order to provide reliable assignments for the transitions to these states. In addition, Hartree—Fock calculations were performed on the lowest five (singlet and triplet) Rydberg states and the 2 Π g state of the positive ion. These results yield an accurate description of the excited states of carbon dioxide and provide for definitive assignments of the transitions observed by optical and electron impact studies (for the five states known experimentally, the calculations agree to within 0.2 eV of the experimental transition energies).

Theoretical determination of the barriers to internal rotation in hydrogen peroxide

The cis and trans barriers to internal rotation in hydrogen peroxide have been accurately determined within the Hartree–Fock approximation using a [4s3pld/2slp] basis set. The calculated trans barrier (384 cm−1) differs from experiment (386 cm−1) by only 2 cm−1. The cis barrier is not well determined by experiment, and the calculated value (2921 cm−1) may well be the most accurate value reported to date. The effects of geometry optimization and polarization functions were also studied. The calculations clearly illustrate the importance of determining the Hartree–Fock geometry for a suitable molecular configuration. With the exception of the OOH bond angle, optimization of the geometrical parameters as the molecule rotates was found to be of little importance; the increase of 6° in &OOH upon rotation from the cis to the trans configuration lowers the cis barrier by 653 cm−1. It was found that the inclusion of oxygen 3d and hydrogen 2p functions was essential for describing the trans barrier, without which ...

Theoretical description of the diimide molecule

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Theoretical assignments of the electronic states of nitrous oxide

C.S. Ewing and D. O. Harris. J. Chem. Phys. 52, 6268.(1970).

An algorithm for the use of symmetry in molecular self-consistent-field calculations

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Formaldehyde Molecule in a Gaussian Basis: Electronic Density

R. H. Hunt, R. A. Leacock, C. W. Peters and K. T. Hecht, J. Chem. Phys. 42, 1931 (1965).

Formaldehyde Molecule in a Gaussian Basis. One‐Electron Properties

The N2H2 molecule is only metastable and as a consequence is not well characterized experimentally. Therefore, we have carried out extensive Hartree−Fock calculations in order to determine equilibrium geometries, one−electron properties, and the relative energies of the cis and trans isomers. In addition, Hartree−Fock and multiconfiguration calculations were carried out to determine the mechanism for isomerization. The trans isomer was found to be 6.6 kcal/mole more stable than the cis form using a basis set which included polarization functions. The lowest energy path found for isomerization occurred by inversion about one nitrogen (rather than rotation about the NN bond) with an activation energy of 47 kcal/mole. Excitation energies for the lowest singlet and triplet excited states are also presented.

Accelerating the convergence of matrix Hartree-Fock calculations

The results of accurate configuration interaction calculations on the excited states of N2O are used to provide accurate assignments of the observed excitation features. Current assignments of the N2O spectra are compared and results for the higher lying valence states are presented. The best values obtained for the excitation energies of the valence states are 3Σ+ (5.4 eV), 3Δ (6.0 eV), 3Σ−(6.5 eV), 1Σ−(6.6 eV) and 1Δ (6.8 eV). This study also provides a comparison of the Hartree-Fock, INDO, and configuration interaction methods.