Roberta P. Saxon

Abinitio configuration interaction study of the valence states of O2

Configuration interaction calculations have been performed for the 62 electronic states of O2 arising from O atoms in the lowest 3P, 1D, and 1S states. The calculations used an extended one‐particle basis set, and included internal and semi‐internal electron correlation effects. Numerical values for potential curves are reported for all states. Detailed comparison with experiment and other calculations is made for the seven lowest bound states: X 3Σg−, a 1Δg, b 2Σg+, c 1Σu−, C 3Δu, A 3Σu+, and B 3Σu−. For these seven states the maximum error in the calculated spectroscopic constants Re, De, Te, and ωe are 0.04 A, 0.4 eV, 0.2 eV, and 120 cm−1, respectively.

Photofragment spectroscopy and potential curves of Ar+2

Photofragment energy distributions have been measured for the process Ar+2(2Σ+u)+hν→Ar++Ar using a 3 keV ion beam and cw lasers both coaxial and crossed with the ion beam, polarized, respectively, perpendicular and parallel to the ion beam direction. Measurements were made at 14 wavelengths between 4579 and 7993 A. Transitions to the dissociative states 2Πg and 2Σ+g are observed, as are the effects of the spin–orbit interaction in Ar+2. The experimental results are used along with theoretical calculations to determine the 2Σ+u, 2Σ+g, and 2Πg potentials. The effects of the spin–orbit interaction on the potential curves, the magnitude and wavelength dependence of the photodissociation cross section, and the angular distributions of the photofragments are considered.

Ab initio calculations for the X 2Σ, A 2Π, and B 2Σ states of NaAr: Emission spectra and cross sections for fine‐structure transitions in Na–Ar collisions

Configuration interaction (CI) calculations were performed for the X 2Σ, A 2Π, and B 2Σ states of NaAr. The A 2Π state is calculated to have a well depth of 492 cm−1 at an internuclear separation of 3.04 A. Small wells of 55 and 32 cm−1 were found for the X 2Σ and B 2Σ states located at 5.01 and 6.80 A, respectively. The spectra for A 2Π–X 2Σ emission in the limits of zero and infinite Ar pressure were calculated and compared with the experiment of York, Scheps, and Gallagher and the predictions using the pseudopotential curves of Pascale and Vandeplanque. The potentials from this work give spectra in much better agreement with experiment than the pseudopotential predictions. Total and differential cross sections for fine‐structure changing transitions Na(2P1/2) +Ar→Na(2P3/2)+Ar−17.2 cm−1 were calculated by a quantum mechanical technique. The total cross sections are in excellent agreement with experimental results. The excited state differential cross sections exhibit prominent rainbow structure centered...

Excited states of CH+: Potential curves and transition moments

Wave functions and potential curves for the ground X 1Σ+ state and eight excited states of 1Σ+ and 1Π symmetry of CH+ have been obtained using ab initio configuration interaction (CI) methods. In order to take proper account of valence–Rydberg mixing, Rydberg functions were included in the basis set. The orbitals used in the set of reference configurations for the CI wave functions included both valence and Rydberg orbitals, determined from a multiconfiguration self‐consistent field and a natural orbital calculation, respectively. Transition moments between the ground electronic state and the 2 1Σ+, 3 1Σ+, A 1Π, and 2 1Π states have been computed, and the importance of these states in photodissociation of CH+ is discussed.

Ab initio calculations of the 3Σg+ and 3Σu+ states of singly excited Ar2

CI calculations were performed for the 3Σg+ and 3Σu+ excimer states of Ar2 using molecular orbitals determined by MCSCF calculations. The 3Σg+ state has a small barrier and shallow well, as expected from analogy with other rare gas dimers. The deeply bound 3Σu+ potential curve has a well depth of 0.68 eV at an internuclear separation of 4.59 ao. Elastic scattering on these curves was calculated and compared with experimental data. The primary rainbow from the 3Σu+ state is found to be in excellent agreement with observation.

Abinitio configuration interaction study of the low‐lying electronic states of MgH

Ab initio configuration interaction calculations have been performed on the X 2Σ+, A 2Π, and B′ 2Σ+ states of MgH. Numerical values for the potential curves have been obtained for 23 internuclear distances between 2.2 and 9.5 a0. Dipole and transition moment functions have also been calculated. Spectroscopic constants obtained from the calculated potential curves are found to be in good agreement with experimental data; the maximum errors in Re, De, Te, and ωe are 0.003 nm, 0.09 eV, 0.05 eV, and 38 cm−1, respectively. The calculated band absorption oscillator strength for the X–A transition of 0.161 is believed to have ±20% accuracy.

Abinitio configuration interaction study of the Rydberg states of O2. II. Calculations on the 3Σg−, 3Σu−, 3Πg, 1Πg, and 1Σg+ symmetries

Using the computational procedure established in the previous paper, configuration interaction calculations have been performed for the 3Σg−, 3Σu−, 3Πg, 1Πg, and 1Σg+ symmetries of O2. The lowest diabatic Rydberg state for each symmetry is presented. Vibrational energy levels of the 1Πg Rydberg state are given. The extent of Rydberg–valence interaction is discussed and the 3Σu− state is compared with a previous calculation.

Theoretical study of low‐lying states of H3O

The first two doublet and quartet states of H3 O have been surveyed by multiconfiguration self‐consistent field/first‐order configuration interaction (MCSCF/FOCI) calculations in C3v symmetry. Geometries of the minima on the doublet surfaces have been optimized by MCSCF gradient techniques and energies obtained by large‐scale multireference single and double excitation CI calculations. The correlation diagram linking the minima to different dissociation limits has been established. A local minimum in C3v symmetry of ion‐pair character is shown to be unstable with respect to dissociation to H2 +H+O. The lowest state, 1 2 A1 in C3v , (1 2 A’ in Cs ) may be characterized as an H3 O+ core surrounded by an oxygen 3s Rydberg electron. Transition states for dissociation of the 1 2 A’ state to H2 O+H and to OH+H2 have been investigated. An extremely low barrier height, 3.58 kcal/mol without vibration, 0.4 kcal/mol for H3 O, an estimated 1.3 kcal/mol for D3 O, with zero‐point energy, is found for dissociation of t...

Abinitio configuration interaction study of the Rydberg states of O2. I. A general computational procedure for diabatic molecular Rydberg states and test calculations on the 3Πg states of O2

Configuration interaction calculations have been performed on the 3Πg symmetry of O2 which establish a general computational procedure for diabatic molecular Rydberg states. Three different calculations which include varying amounts of electronic correlation for the Rydberg and valence states are reported. The interaction potentials for the lowest diabatic Rydberg state from these three calculations are in excellent agreement showing that semi‐internal correlation energy of Rydberg states has little effect on the potential curves. The Rydberg state is found to be exceedingly similar to the O2+ 2Πg state to which the 3Πg Rydberg series converges. Energies for the lowest four Rydberg vibrational levels are presented.

Elastic scattering measurements of the Ar2* (3Σ+u) well depth

Angular distribution measurements of the scattering of Ar(3P2) from Ar(1S0) at center of mass collision energies from 5 to 10 eV yield a prominent rainbow maximum at τ=Eϑ=81±3 eV‐deg. Combined with recent high energy ground state scattering data and information derived from the Ar2* emission continua, the result implies that De=0.78±0.04 eV and Re=2.33±0.02 A in an assumed Morse form for the lowest 1u, 0−u(3Σ+u)Ar2* excimer potential.