William R. Rodwell

Dipole moment functions of the hydrogen halides

Experimental intensity data for vibration–rotational transitions and molecular beam data of the hydrogen halide diatomic molecules (HF, HCl, HBr, and HI) have been analyzed, and the coefficients of a power series expansion of the dipole moment functions valid near the equilibrium internuclear separations have been determined. Ab initio quantum chemical computations of the dipole moments have also been carried out over a wide range of internuclear separations for HF, HCl, and HBr, and the factors affecting the accuracy of these results have been critically examined. The long‐range values from these computations have been combined with the results near equilibrium in the form of a Pade approximant that embodies the correct asymptotic behavior.

The Hartree–Fock geometry of ammonia

Ammonia is one of those small molecules which have been used as ’test cases’ in the development of molecular electronic structure calculations. It is important to characterize the geometry in Hartree‐Fock limit. Such a study of the equilibrium geometry of ammonia is reported. (AIP).

Influence of basis set and electron correlation on calculated barriers to 1,2-hydrogen shifts. The oxoniomethylene cation: A new CH3O+ isomer?

Abstract Ab initio molecular orbital theory has been used to study the intramolecular rearrangement of ethylidene to ethylene and of the oxoniomethylene cation to the hydroxymethyl cation. Optimized geometries of stable isomers and transition structures have been determined using gradient procedures and the 4-31G basis set. Improved energy comparisons have been obtained with the double-zeta plus polarization 6-3IG ++ basis set with electron correlation incorporated at the levels of second- (MP2) and third- (MP3) order Moller—Plesset perturbation theory.

Theoretical studies of the effect of electron correlation on the geometry and barriers to internal rotation in hydrogen peroxide

Abstract The effect of electron correlation on the geometries of the skew , cis and trans conformations of H 2 O 2 and on the heights of the barriers to internal rotation has been investigated by means of ab initio strongly orthogonal geminal (APSG) calculations using a high quality gaussian basis set. The intrapair correlation included in the APSG method accounts for the deficiencies in previous SCF predictions of the equilibrium geometry for H 2 O 2 , and with the exception of the OO bond length, which is overcorrected, the calculated geometrical parameters agree well with experimental values. The calculated barriers to internal rotation are little affected by the inclusion of electron correlation and in particular the experimentally poorly characterised cis barrier is predicted to be 35 kJ/mol, supporting the previous best SCF result. Selected calculated one-electron properties for H 2 O 2 are also reported.

Structures and thermodynamic stabilities of the C2H4O isomers: Acetaldehyde, vinyl alcohol and ethylene oxide

Ab initio molecular orbital theory with a sequence of basis sets ranging from minimal to triple zeta plus polarization and with electron correlation incorporated using Möller-Plesset perturbation theory terminated at third order (MP3) is used to examine the structures and relative energies of the C2H4O isomers, acetaldehyde, vinyl alcohol and ethylene oxide. Acetaldehyde is indicated to be the most stable isomer with vinyl alcohol lying 45 kJ mol−1 and ethylene oxide 114 kJ mol−1 higher in energy. The theoretical structures and energies are in reasonable agreement with the best available experimental data.