Approximate electronic structure calculations on the ground state of the BNB molecule are subject to artifactual symmetry breaking as well as a potential second-order Jahn-Teller distortion along its antisymmetric stretch coordinate. In addition, the bending mode is very floppy and has a large anharmonic coupling with the symmetric stretch. Hence, this molecule presents a major challenge for theoretical electronic structure methods. We present a series of calculations designed to distinguish the real from the artifactual symmetry breaking. Our results give the minimum structure as C-infinityv, with the D-infinityh transition state 161 +/- 20 cm(-1) higher in energy, thus lying below the first vibrational level. [References: 36]
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