Raman spectroscopy and ab initio quantum chemical calculations of ion association behavior in calcium nitrate solution

In this work, microscopic Raman spectroscopy and component analysis were used to study a calcium nitrate solution with molar water‐to‐salt ratio (WSR) values of 4–320. The results showed that the symmetrical stretching vibration wavenumber of the nitrate ion (v1‐NO3−) in the solution blue shifted from 1,048 to 1,053 cm−1, and the full width at half maximum increased from 9.7 to 11 cm−1 when the WSR was reduced from 320 to 4. The component analysis of v1‐NO3− showed that the first concentration region was for WSR ≥ 16.3. In this region, solvent‐shared ion pairs (SIPs) were the main species, and contact ion pairs (CIPs) and free‐hydrated ions were the secondary species. For 8.4 ≤ WSR