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  • Title: Characterization of the BNNO Radical.
    Author: Cheng Q, Simmonett AC, Evangelista FA, Yamaguchi Y, Schaefer HF.
    Journal: J Chem Theory Comput; 2010 Jun 08; 6(6):1915-23. PubMed ID: 26615850.
    Abstract:
    The cyclic, trans, and cis BNNO molecules and the two isomerization reactions on their doublet electronic states potential energy surface (PES) are systematically investigated. Ab initio self-consistent field, complete active space self-consistent field, coupled cluster with single and double excitations (CCSD), and CCSD including perturbative triple excitations [CCSD(T)] quantum mechanical techniques are employed, in conjunction with Dunning's correlation consistent polarized valence basis sets (cc-pVXZ and aug-cc-pVXZ, where X = D, T, and Q). All stationary points located on the doublet PES lie within 19 kcal mol(-1) of the global minimum cyclic isomer at the aug-cc-pVQZ CCSD(T) level of theory. The cyclic and trans minima are separated by 2.4 kcal mol(-1) with an interconversion barrier (cyclic → TS2 → trans) of 18.3 kcal mol(-1); the trans and cis isomers are separated by 10.4 kcal mol(-1) with a barrier (trans → TS1 → cis) of 10.4 kcal mol(-1). The dissociation energies BNNO (X̃ (2)A') → B ((2)Pu) + NNO (X̃ (1)Σ(+)) for the cyclic, trans, and cis isomers are predicted to be 39.7, 37.3, and 27.0 kcal mol(-1), respectively. The diatomic fragment dissociation energies BNNO (X̃ (2)A') → BN (X (3)Π) + NO (X (2)Σ(+)) for the three isomers are determined to be 50.7, 48.4, and 38.0 kcal mol(-1), respectively. Additionally, fundamental vibrational frequencies are computed for the cyclic and trans isomers through application of second-order vibrational perturbation theory (VPT2) at the cc-pCVTZ CCSD(T) level of theory. Comparison of the resulting vibrational frequencies and their isotopic shifts with those determined experimentally by Wang and Zhou yields the surprising result that the B ((2)Pu) + NNO (X̃ (1)Σ(+)) reaction leads to formation of the trans isomer. The latter structure is not the global minimum, rather the second lowest lying isomer. This apparent disparity is rationalized by detailed examination of the PES describing this reaction.
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