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

摘要

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.