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Theoretical studies on sulfur-containing radical ions

Carmichael I.

Nukleonika

2000

Vol. 45, nr 1

11-17

Structures and properties are reported for pi-radical cations and for sigma-radical cations and anions, containing SS, SN and SO odd-electron bonds, from a variety of ab initio molecular orbital techniques and Density Functional Theory (DFT). Characteristic frequencies and absorption bands are determined to aid in the assignment of transient vibrational and optical spectra detected in pulse radiolysis experiments. Hyperfine coupling tensors are evaluated to facilitate the identification of these radicals by EPR spectroscopy. By comparison with predictions from accurate coupled-cluster based calculations in some simple model systems, DFT is shown to have difficulties in correctly describing the electronic structure of these radical ions. Useful linear relationships are uncovered between the computed lenght of the odd-electron bond and both the wavelenght of maximum optical absorption and the bond stretching frequency.

The ground state of (He-H-He)(+) from correlated ab initio calculations

Komasa J., Rychlewski J.

Polish Journal of Chemistry

1998

Vol. 72, nr 7S

1353-1360

He2H(+) ion in its ground state is studied by means of ab initio methods taking into account the electron correlation. Geometry optimization at the CCSD(T)/cc-pV5Z level of theory has been performed and the potential energy hypersurface scan is presented. The optimum conformation is linear and symmetric with the proton at the He-He midpoint and the He-H distance equal to 1.75 bohr. Stabilization energy with respect to the He2H(+) --- HeH(+) + He dissociation channel has been computed. Additionally, a single point variational calculations with the use of the Exponentially Correlated Gaussian wave functions have been performed. They supply an upper bound to both the total electronic energy (-5.903505 hartree) and the stabilization energy (-13.224 kcal/mol). A comparison of the results from both the perturbational coupled cluster and variational methods is presented.

Electron affinity of CH3 and BH3 and structure of their anions

Gutsev G.L., Bartlett R.J.

Polish Journal of Chemistry

1998

Vol. 72, nr 7S

1604-1614

The electronic and geometrical structure of the methyl radical, CH3, the borane molecule, BH3, as well as their anions CH3(-) and BH3(-) are calculated with the Hartree-Fock Density Functional Theory (HFDFT), fourth-order many-body perturbation theory (MBPT(4)), and the coupled-cluster (CCSD(T)) methods with the use of the large atomic natural orbital basis of Widmark-Malmqvist-Roos. Petential energy surfaces of BH3 and BH3(-) symmetric stretchings and out-of-plane C3v hydrogen motions of CH3 and CH3(-) are obtained at the MBPT (4)/6-311++G(3df, 3pd) level. At the CCSD(T) level of theory, the difference in the total electronic energies of CH3 and CH3(-) is 0.01 eV and that of BH3 and BH3(-) is -0.05 eV. Corrected for the zero-point energies (ZPE) of nuclear motions, the adiabatic electron affinities (EA-ad) of CH3 and BH3 are 0.05 and 0.01 eV, respectively, being in nice agreement with the experimental values of 0.08(+/-)0.03 and 0.038(+/-)0.015, respectively. Thus, the EA-ads of CH3 and BH3 are defined mainly by the differences in the ZPEs of the corresponding neutral-anion pairs.