Proton tunneling in the strong hydrogen bonds in the solid state

In low dimensional caesium silicate LDS-1 (monoclinic phase of CsHSi2O5), anomalous infrared absorption bands observed at 93, 155, 1210, and 1220 cm-1 are assigned to the vibrational mode of protons, which contribute to the strong hydrogen bonding between terminal oxygen atoms of silicate chain with the O–O distance of 2.45 Å. The integrated absorbance (oscillator strength) for those modes is drastically enhanced at low temperatures. The analysis of integrated absorbance employing two different anharmonic double-minimum potentials makes clear that proton tunnelling through the potential barrier yields an energy splitting of the ground state. We propose to employ the neutron Compton (NCS) scattering to observe the onset of the proton tunnelling in a single-crystal specimen of LDS-1.