Effect of Deuteration on Raman Scattering in Single Crystals of Potassium Alum

Abstract

Raman spectra of KAl(SO₄)₂·12H₂O and KAl(SO₄)₂·12D₂O crystals in the range of 10–4000 cm⁻¹ were experimentally obtained and studied. An increase in the number of sulfate ions, oriented by oxygen atoms towards the K⁺ ion, was detected upon deuteration of the sample. Low-intensity Stokes components ν = 2485 cm⁻¹ (ν = 1820 cm⁻¹ for the deuterated crystal) were recorded, which indicates the formation of hydrogen bonds O–H•••SO₄²⁻ (O–D•••SO₄²⁻), where the donors are water molecules of the [Al(H₂O)₆]³⁺ complex and the oxygen atoms of the sulfate ion act as acceptors. The decrease in the wavenumbers of internal vibrations of the sulfate ion during deuteration was explained by an increase in the strength of hydrogen bonds. The results obtained indicate the direct influence of deuteration on the degree of initial disordering of sulfate ions and on the stability of the crystal structure of potassium alum.