Geometric Isotope Effect on Low Barrier Hydrogen-Bonding Systems of Acetic Acid Dimer, Formic Acid Dimer, and Their Anionic Clusters by Using the Multi-Component Molecular Orbital Method

Masato KANEKOa, Taro UDAGAWAa,b and Masanori TACHIKAWAa,c*

aQuantum Chemistry Division, Graduate School of Science, Yokohama-city University
bPresent address: Department of Chemistry, Faculty of Engineering, Gifu University
cCREST, Japan Science and Technology Agency
Honcho 4-1-8, Kawaguchi, Saitama 332-0012, Japan

(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.

キーワード: Geometric isotope effect, Low barrier hydrogen bond, Multi-component molecular orbital method, Acetic acid dimer, Formic acid dimer

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