二钼酸铵晶体饱和水溶液Raman光谱的变异现象及其机理

记录了常温下二钼酸铵晶体饱和水溶液的Raman光谱，并分别与二钼酸铵晶体、仲钼酸铵晶体、仲钼酸铵晶体饱和水溶液、水溶液状态下单钼酸根离子的Raman光谱进行了比较研究。结果表明：二钼酸铵晶体饱和水溶液Raman光谱相对二钼酸铵晶体Raman光谱，明显地发生了变异现象。二钼酸铵晶体饱和水溶液Raman光谱其主要特征峰最高振动频率937.6 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征峰最高振动频率937.6 cm^-1完全吻合，而其次高振动频率893.9 cm^-1，恰好介于水溶液中单钼酸根离子Raman光谱主要特征峰最高振动频率895.1 cm^-1与仲钼酸铵晶体饱和水溶液Raman光谱主要特征次高峰振动频率891.0 cm^-1之间，而且三者彼此接近。二钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值为2.1，与仲钼酸铵晶体饱和水溶液Raman光谱主、次特征峰强度之比值4.4相比，一半不足。提出了一种利用Raman光谱主要特征峰振动频率及其主、次特征峰强度之比值对二钼酸铵晶体饱和水溶液组分同时进行定性和半定量分析的新方法。发现了常温下二钼酸铵晶体饱和水溶液中二钼酸根离子Mo₂O₇^2-已经不复存在，完全转变成了优势组分仲钼酸根离子Mo₇O₂₄^6-和次要组分单钼酸根离子MoO₄^2-；证明了常温下含钼水溶液酸化过程中溶液Raman光谱离散性变化现象的存在。运用结构化学和物理化学原理同时讨论了二钼酸铵晶体饱和水溶液Raman光谱发生变异现象的机理。

Aberrant Phenomenon of Raman Spectrum of Saturated Aqueous Solution of Ammonium Dimolybdate Crystal as well as Its Mechanism

Raman spectrum of saturated aqueous solution of ammonium dimolybdate crystal was recorded, and compared with those of ammonium dimolybdate crystal, ammonium heptamolybdate crystal, saturated aqueous solution of ammonium heptamolybdate crystal and monomolybdate anion in aqueous solution respectively. The results showed that the aberrant phenomenon occured obviously concerning the relation of Raman spectrum of saturated aqueous solution of ammonium dimolybdate crystal to that of ammonium dimolybdate crystal. The value 937.6 cm^-1 of the highest vibrant frequency of Raman spectral main characteristic peak of saturated aqueous solution of ammonium dimolybdate crystal was completely in accordance with that of saturated aqueous solution of ammonium heptamolybdate crystal. The value 893.9 cm^-1 of the second high vibrant frequency of Raman spectral main characteristic peak of saturated aqueous solution of ammonium dimolybdate crystal was located just between the value 895.1 cm^-1 of the highest vibrant frequency of Raman spectral main characteristic peak of monomolybdate ion in aqueous solution and the value 891.0 cm^-1 of the second high vibrant frequency of Raman spectral main characteristic peak of saturated aqueous solution of ammonium heptamolybdate crystal. The Raman spectral intensity ratio of the highest vibrant frequency to the second vibrant frequency of saturated aqueous solution of ammonium dimolybdate crystal was 2.1, which was less than that half of the intensity ratio 4.4 of saturated aqueous solution of ammonium heptamolybdate crystal. A new method of qualitative and half quantitative analysis of saturated aqueous solution of ammonium dimolybdate crystal according to main characteristic vibrant frequencies and the intensity ratio of Raman spectral two main characteristic peaks was put forward. It was found that dimolybdate ion did not exist in the saturated aqueous solution and was transformed into heptamolybdate ion Mo₇O₂₄^6- as the predominant species and monomolybdate ion MoO₄^2- as the secondary species. This work well proved the existence of discrete change phenomenon of Raman spectra of acidified molybdate aqueous solution.The mechanism of the aberrant phenomenon was discussed by using principles of structural chemistry and physical chemistry. This new analytical methoth is right-reliable and simple-feasible, and has important roles in studying chemical process equilibrium of slight acidification and first polymerization of molybdate solution abstracted from molybdate ores with ammonia water and in exploring the new best technical condition of industrial production of ammonium heptamolybdate.