Isotope effects and Fermi resonance in hydrogen bonds—hydrogen potential and wave function

Abstract

Neutron-scattering measurements on a hydrogen-bonded compound, KHCO 3, with a bond length of about 2.6 Å were performed, and the intensity maps of the scattering function ( S( Q, ε)) observed over a very wide energy–momentum region of 0< ε<500 meV and 0<| Q|<20 Å −1. From these intensity maps, we succeeded in obtaining the real-space distribution of the hydrogen wave function at the excited states for the first time. Their distribution maps were compared with the calculated ones, using a theoretically proposed potential model. It provided strong support for the proposed potential itself, and also provided a direct evidence of a Fermi resonance which was predicted to be a major feature of all O–H–O bonds of about 2.6 Å length.