常温高压下碳酸根离子的拉曼谱峰标定压力初探

在准静水压的条件下，利用碳化硅压腔和显微拉曼光谱原位测量技术，在0～1.7 GPa压力范围测定22 ℃高压下三种不同的H₂O-Na₂CO₃体系(1.5，2.0，2.5 mol·L-1)中CO2-₃的对称伸缩振动ν_{1 066}拉曼谱峰的变化。结果表明，在室温条件下，碳酸根的ν_{1 066}峰的拉曼位移随着压力的增大而线性增加。三种浓度下ν_{1 066}峰的拉曼位移与压力的拟合直线彼此接近，斜率误差小于1%，偏差小于系统误差，因此在实验误差范围内碳酸根浓度对ν_{1 066}峰随压力变化的行为不存在影响。经过数据拟合得到公式：p/MPa=174.13 Δν_{1 066}/cm-1—59.03(Δν_{1 066}=ν_{1 066}-ν_{1 066}0,ν_{1 066}0为体系零压时碳酸根离子ν_{1 066}峰的拉曼位移)。此公式可以用于常温下在含有纯碳酸钠体系中的压力标定。

Raman Spectra of Carbonate Ions as Pressure Gauge at High Pressure and Room Temperature

Three aqueous solutions of sodium carbonate (1.5, 2.0 and 2.5 mol·L-1) were studied by in-situ Raman spectrum in a moissanite anvil cell in order to measure the Raman shift of symmetric stretching vibration of carbonate ion at around ν_{1 066}. The experiment was conducted from 0 to 1.7 GPa under quasihydrostatic conditions at temperature of 22 ℃. The result showed that the increase in Raman wavenumber shift of in-plane bending vibration of carbonate ion is linearly proportional to the rise of pressure under room temperature. At the three concentrations mentioned above, the correlations between Raman shift of the ν_{1 066} peak and the pressure are depicted as three nearly identical curves, with a slope error smaller than 1%. The deviation, being smaller than the systemic error, suggested that the concentration of carbonate ions, within experimental errors, has no detectable influence on the pressure-induced shift of ν_{1 066} peak. Besides, the data fitting generated the formula: p/MPa=174.13Δν_{1 066}/cm-1-59.03(Δν_{1 066}=ν_{1 066}-ν0_{1 066},where ν0_{1 066} denotes the Raman shift of ν_{1 066} peak of carbonate ion under the ambient pressure, which can be used as a pressure gauge in pure Na2CO₃ solution.