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Why Is Methylene a Ground State Triplet while Silylene Is a Ground State Singlet?

Summary: Why Is Methylene a Ground State Triplet while Silylene
Is a Ground State Singlet?
Yitzhak Apeloig,*, Ruben Pauncz, Miriam Karni, Robert West,
Wes Steiner, and Douglas Chapman*,
Department of Chemistry and the Lise Meitner-Minerva Center for Computational Quantum
Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel, Department of
Chemistry, University of Wisconsin, Madison, Wisconsin 53706, and Department of Chemistry,
Southern Oregon University, Ashland, Oregon 97520
Received April 9, 2003
The singlet-triplet energy difference in CH2 and SiH2 was calculated at the CASSCF level
of theory using large Gaussian basis sets that included f-type functions. The total energy
was separated into nuclear repulsion and electronic energy, and the latter was further
decomposed into the contributions coming from the two electrons highest in energy (the
"frontier" electrons, denoted by "f") and from all the other electrons (denoted by "c" for "core").
The contribution of the frontier electrons was further decomposed into the following terms:
, which is the sum of the kinetic energy and the attraction energy to the nucleus of the
two frontier electrons and their repulsion energy from all other electrons, and Eee
, the


Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology


Collections: Chemistry