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Area of Science:

  • Quantum Chemistry
  • Computational Chemistry
  • Chemical Physics

Background:

  • Free radicals exhibit spin polarization in their core electrons.
  • Understanding spin polarization is crucial for predicting radical reactivity and properties.

Purpose of the Study:

  • To demonstrate the cooperative nature of spin polarization in the core of free radicals.
  • To investigate the non-additive effects of spin polarization in chemical bonds.
  • To explore the implications of this phenomenon in diradicals.

Main Methods:

  • Configuration interaction calculations up to the full valence limit.
  • Analytic theoretical developments.
  • Case studies including the methyl radical (CH3) and carbo-cyclobutadiene (C12H4).

Main Results:

  • Spin polarization in CH sigma bonds is cooperative, with polarization in one bond enhancing that in neighboring bonds.
  • This cooperative effect was confirmed through extensive computational calculations.
  • The phenomenon was also observed in diradicals like carbo-cyclobutadiene, where spin polarization is significant.

Conclusions:

  • The spin polarization of closed-shell cores in free radicals is a cooperative phenomenon.
  • This cooperativity presents challenges for standard computational chemistry methods (post-Hartree-Fock).
  • The findings offer new insights into the electronic structure and behavior of radical species.