Isotope effect in dihydrogen-bonded systems: Application of the analytical energy gradient method in the nuclear orbital plus molecular orbital theory

Hiromi Nakai, Yasuhiro Ikabata, Yasuhiro Tsukamoto, Yutaka Imamura, Kaito Miyamoto, Minoru Hoshino

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We investigate isotope effects in dihydrogen systems using the nuclear orbital plus molecular orbital (NOMO) theory, which simultaneously determines nuclear and electronic wave functions without the Born-Oppenheimer approximation. In order to estimate the vibrational averaging bond distances, the analytical energy gradients are used for the NOMO theory. The bond distances of three dihydrogen-bonded systems, namely H3NX+ XBeH, LiX XC2H and H2BX XF for X = H, D and T, are obtained. The X X bond distances decrease with respect to the substitution T D H, which is contrary to the behaviour of typical hydrogen bonds. This indicates that isotope effects strengthen the X X bond. This behaviour is analogous to the Ubbelohde effect observed in the solid phase.

Original languageEnglish
Pages (from-to)2649-2657
Number of pages9
JournalMolecular Physics
Issue number19-22
Publication statusPublished - 2007 Oct 21



  • Analytical energy gradient
  • Dihydrogen-bonded system
  • Isotope effect
  • Nuclear orbital plus molecular orbital theory
  • Vibrational averaging shift

ASJC Scopus subject areas

  • Biophysics
  • Molecular Biology
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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