The Stretching Frequencies of Isotopic Arsenate and Permanganate Ions in Aqueous Solutions

The infrared absorption of crystalline powders and D₂O solutions of normal and 84.5 atom % ¹⁸O-labelled sodium arsenate as well as normal and 83.3 atom % ¹⁸O-labelled sodium permanganate was measured in the 780–980 cm^?1 region. The ν₁ and ν₃ fundamentals of the aqueous As¹⁸O₄^3? ion appear at 834(sh) and 866(s) cm^?1 while the respective As¹⁸O₄^3? values are 808 and 822 cm^?1 These as well as other data are shown to indicate that the water molecules which hydrate this ion are attached to its As atom. The ν₃ frequency of the aqueous Mn¹⁸O₄^? ion is observed at 917 cm^?1 and that of hydrated Mn¹⁸O₄^? at 878 cm^?1.