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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 24, Number 6
BKCSDE 24(6)
June 20, 2003 

The Potential Energy Surface of BH5 and the Rate of the Hydrogen Scrambling
Kyung Hyun Kim, Yongho Kim
BH5, Hydrogen scrambling, MCMM, Rate constant
The BH5 molecule, which is suggested as an intermediate of the acidolysis of BH4-, contains a weak twoelectron-three-center bond and it requires extremely high-level of theories to calculate the energy and structure correctly. The structures and energies of BH5 and the transition state for the hydrogen scrambling have been studied using recently developed multi-coefficient correlated quantum mechanical methods (MCCMs). The dissociation energies and the barrier heights agree very well with the previous results at the CCSD(T)/ TZ(3d1f1g, 2p1d) level. We have also calculated the potential energy curves for the dissociation of BH5 to BH3 and H2. The lower levels of theory were unable to plot correct potential curves, whereas the MCCM methods give very good potential energy curves and requires much less computing resources than the CCSD(T)/ TZ(3d1f1g,2p1d) level. The potential energy of the BH5 scrambling has been obtained by the multiconfiguration molecular mechanics algorithm (MCMM), and the rates are calculated using the variational transition state theory including multidimensional tunneling approximation. The rate constant at 300 K is 2.1 × 109 s-1, and tunneling is very important.
763 - 770
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