Qualitative and quantitative Raman and infrared (IR) measurements on NaNO3 solutions have been carried out over a wide concentration range (5.56 · 10-6 â 7.946 mol/L) in water and heavy water. The Raman spectra were measured from 4000 cm-1 to low wavenumbers at 45 cm-1. Band fit analysis on the profile of the 1047 cm-1 â band, ν1(a1') NO3- measured at high resolution at 0.85 cm-1 produced a small contribution at 1027 cm-1 of the isotopomer N16O218O-(aq). The effect of solute concentration on the Raman and IR bands has been systematically recorded. Extrapolation of the experimental data resulted in values for all the nitrate-bands of the âfreeâ i.e. fully hydrated NO3-(aq). However, even in dilute solutions the vibrational symmetry of the hydrated NO3-(aq) is broken and the antisymmetric N-O stretch, which is degenerate for the isolated anion, is split by 56 cm-1. At concentrations > 2.5 mol/L direct contact between Na+ and NO3- was observed and accompanied by large band parameter changes.DFT calculations on NO3-(H2O)n (n=1-3) led to optimized geometries and vibrational frequencies which reproduced the measured ones within an accuracy of 1%. A hydrated gas phase species Na+(H2O)10NO3- was optimized resulting in the geometry and symmetry of the nitrate which is bound in an antisymmetric bidentate fashion with the nitrate possessing C1. The ν1 Na+-(OH2) breathing mode in aqueous solution appears at 189 cm-1 whereas in heavy water ν1 Na+-(OD2) is shifted to 175.6 cm-1 due to the isotope effect. DFT calculations on hydrated Na+(OH2)n gas phase clusters provided realistic Na+-hydrate structures with n = 4 and 5 which resembled the measured frequency of ν1 Na+-OH2 mode quite well.Quantitative Raman analysis employing the symmetric stretching band, ν1(a1') NO3-, has been carried out down to concentrations as low as 5.56 · 10-6 mol/L. The in-plane deformation mode ν4(e') in the Raman scattering at higher concentrations has been used as an indicator band for detecting directly coordinated NO3-.

中文翻译：

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EXPRESS：NaNO ₃ (aq) 的水合和离子对形成：振动光谱和密度泛函理论研究

NaNO3 溶液的定性和定量拉曼和红外 (IR) 测量已在水和重水中的较宽浓度范围 (5.56·10-6·7.946 mol/L) 内进行。拉曼光谱是从 4000 cm-1 到 45 cm-1 处的低波数测量的。波段拟合分析 1047 cm-1 â 波段，λ1(a1') NO3- 以高分辨率在 0.85 cm-1 处测量，在 1027 cm-1 处对同位素 N16O218O-(aq) 的贡献很小。已经系统地记录了溶质浓度对拉曼和红外波段的影响。对实验数据的外推得出“游离”即完全水合的 NO3-(aq) 的所有硝酸盐带的值。然而，即使在稀溶液中，水合 NO3-(aq) 的振动对称性也被破坏，反对称 NO 拉伸，对于孤立的阴离子来说是简并的，被 56 cm-1 分割。在浓度 > 2.5 mol/L 时观察到 Na+ 和 NO3- 之间的直接接触并伴随着大的波段参数变化。对 NO3-(H2O)n (n=1-3) 的 DFT 计算导致优化的几何形状和振动频率，重现了测量精度在 1% 以内。对水合气相物质 Na+(H2O)10NO3- 进行优化，导致硝酸盐的几何形状和对称性以反对称双齿方式与具有 C1 的硝酸盐结合。189 cm-1 水溶液中的 Ψ1 Na+-(OH2) 呼吸模式出现在重水中 Ψ1 Na+-(OD2) 由于同位素效应转移到 175.6 cm-1。水合 Na+(OH2)n 气相簇的 DFT 计算提供了现实的 Na+-水合物结构，n = 4 和 5，这与 1 Na+-OH2 模式的测量频率非常相似。定量拉曼分析采用对称伸缩带，λ1(a1') NO3-，已进行到浓度低至 5.56 · 10-6 mol/L。较高浓度的拉曼散射中的平面内变形模式 λ4(e') 已被用作检测直接协调的 NO3-的指示带。