SOME ABINITIO VALENCE-BOND CALCULATIONS FOR NO2

The results of some STO-6G valence-bond calculations, with single-zeta and double-zeta basis sets, are reported for the ground state of NO2. 18 Lewis structures that differ in the locations of the four pi electrons and the odd electron are included in the main calculations, subsequent to the determination of the approximate structure of the sigma-electron core via energy optimization with a smaller number of structures. Regardless of the nature of the orbital basis set in the 18 structure calculations, the spin-paired diradical structure A, [GRAPHICS] as well as structures of types B and C, [GRAPHICS] is calculated to be a primary contributor to the resonance scheme. Therefore, NO2 has considerable spin-paired diradical as well as free-radical character. The results of some single-zeta VB calculations are also reported for CO2-, and consideration is given to the increased-valence and non-paired spatial orbital representations for the pi electrons of NO2. One formulation of the wavefunction for resonance between the increased-valence structures is equivalent to the best linear combination of the wavefunctions for the 18 Lewis structures.