(Received: July 16, 2009; Accepted for publication: October 13, 2009)
Dedicated to the late Prof. Kazuhide MORI.
The geometric isotope effect (GIE) on low barrier hydrogen-bonded systems of acetic acid dimer, formic acid dimer, and their anion clusters is analyzed by HF and hybrid DFT levels of the multi-component molecular orbital (MC_MO) method, which directly includes nuclear quantum effect of proton/deuteron. Our optimized geometries for both neutral and anionic species with HF level of MC_MO method have reproduced the overall tendency of the GIE of the corresponding experimental ones. On the other hand, the results for anionic clusters with hybrid BHandHLYP functional of MC_MO method give poor agreement due to the underestimation of the barrier height of hydrogen-bonding. Our multi-component analysis clearly demonstrates that the hydrogen-bonding interaction energy is strongly affected by the distribution of nuclear wavefunction.
$B%-!<%o!<%I(B: Geometric isotope effect, Low barrier hydrogen bond, Multi-component molecular orbital method, Acetic acid dimer, Formic acid dimer
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