Stephen Rothenberg

Theoretical Study of SO2 Molecular Properties

Using two contracted Gaussian functions for each atomic orbital, plus d functions on both sulfur and oxygen to describe molecular charge distortion, a self‐consistent‐field wavefunction was computed for the 1A1 ground state of SO2. It is estimated that the calculated SCF energy, − 547.2089 hartree, lies no more than 0.1 hartree above the Hartree–Fock energy for SO2. An additional calculation without d functions and population analyses indicate that (a) d functions on sulfur are much more important in SO2 than was the case in previous work on H2S and (b) in SO2, d functions on sulfur are much more important than those on oxygen. Calculated molecular properties are in good agreement with available experimental data. Of particular importance is the fact that the calculated elements of the molecular quadrupole moment tensor are 31%, 30%, and 29% greater than those recently determined experimentally by Pochan, Stone, and Flygare. Values of the third moments, octupole moment tensor, diamagnetic shielding tensor...

Natural Orbitals for Hydrogen‐Molecule Excited States

The technique of analyzing a many‐configuration wavefunction into natural orbitals has been extended to the excited states of H2. All of the low‐lying singly excited electronic states up to a principal quantum number of 3 have been investigated and the natural orbitals are given. Plots of some of the orbitals are included to facilitate visualization of the results. From calculated singlet—triplet splittings, it is suggested that the spectroscopic assignment of the triplet levels is approximately 110–140 cm−1 too high for H2.

Self-consistent-field wave functions, energies, multipole moments, diamagnetic susceptibility and shielding tensors, and electric field gradient tensors for nitrogen dioxide and ozone

Using basis sets of ‘ double zeta plus polarization ’ quality, non-empirical self-consistent-field calculations have been carried out on the ground states of NO2 and O3. The computed total energies, -204·0679 and -224·3093 hartree, are the lowest reported to date for these molecules and are estimated to lie about 0·06 hartree above the respective Hartree-Fock limits. Calculations were also carried out without d (or polarization) functions and it was determined that (a) d functions are about three times more important on the central atom than on the terminal oxygens in both molecules and (b) d functions are 2·5 to 3 times less important in O3 than in SO2. Calculated second moments of the electronic charge distribution and diamagnetic susceptibilities are in good to excellent agreement with experiment for ozone. Dipole moments for both molecules and quadrupole coupling constants for NO2 are only in qualitative agreement with experiment. The calculated molecular quadrupole moments of O3, for reasons not unde...

Theoretical intensities for the X1Σg+-np1Πu transitions of H2. A study of the Franck-Condon principle

Abstract The recent availability of accurate electronic and vibrational wave funetions for several H 2 excited states permits an explicit test of the validity of the Franck-Condon prineiple within the Born-Oppenheimer approximation. The transitions from the ground-electronic state ( 1 Σ g + ) to the 1 s 2 p , 3 p , and 4p 1 Π u excited states all are found to have intensities that differ by less than 10% from those predicted by using the Franck-Condon principle. The Condon parabola is presented for the transition from the ground state to the 2 p state. Band-averaged oscillator strengths are given for the transition from the ground state to the 2 p , 3 p , and 4p 1 Π u states and the 2 p and 3p 1 Σ u + states In addition, the use of the natural orbital expansion of the electronic wave function has revealed that the correlation terms in the wave function have a rather small role in determining the value of the dipole transition moment (less than 15%).

Theoretical Study of the Barriers to Internal Rotation in Formic Acid

Nitrous acid, HONO, has been studied for three geometries by the ab initio LCAO SCF MO method with a basis of accurate gaussian atomic orbitals. The trans geometry is correctly predicted to be most stable, lying about 2 kcal/mole lower than the cis form, and 9 kcal/mole lower than the 90° form (experimental estimates being 0.4 and 11.6 kcal/mole, respectively). Population analysis, dipole moment components, and properties related to nuclear-nuclear and nuclear-electron potentials all show a partial breaking of the hydroxyl oxygen-nitrogen bond at 90° compared to cis and trans, as well as the effects of electronic rearrangement for nuclear screening in the high nuclear repulsion cis form. The cis to 90° barrier is dominated by the attractive components of the total energy, while the trans to 90° one is dominated by repulsive components, in agreement with our analysis and an earlier prediction by Allen.

HCl and HF proton donors: a theoretical study

Abstract The proton donor ability of HCl and HF are compared by carrying out ab initio molecular orbital studies on complexes of these proton donors with a number of proton acceptors. In addition, the structure and H-bond energy of the HCl dimers and HCl-HF complexes are predicted.

Hydrogen‐Molecule Excited States: 1Πu

The four lowest‐lying electronic states of molecular hydrogen of 1Πu symmetry have been calculated theoretically within the Born—Oppenheimer framework. The potential curves are quite regular, exhibiting maxima in the lowest state (2pΠu) at 8.85 bohr of about 120 cm−1 and the third state (4fΠu) at 5.9 bohr of about 715 cm−1. The potential curves have been used to calculate the vibrational—rotational energy levels for those states.