NaCl-O2体系高温高压化学反应的拉曼光谱证据

摘要

利用金刚石压腔装置和显微激光双面加热技术,对NaCl-O 2体系在高温高压下的化学反应进行研究.在55 GPa下对样品进行激光加热,使温度达到1500~2000 K,然后在常温下对产物进行拉曼光谱测量.测试数据显示,NaCl-O 2体系在上述温压条件下发生了化学反应,产物包括NaO4、NaCl3等非传统化合物,以及少量的NaClO4和中间产物Cl2.易吸潮的NaO4黑色粉末在常压下仍稳定存在,其1384 cm-1特征振动峰反映其结构中存在带分数负电荷的O-O原子对.斜方结构NaCl3表现出强的拉曼信号,可分辨出10个拉曼峰,并在卸压过程中于23 GPa左右完全分解为NaCl+Cl2.实验结果表明,高压有利于O元素和Cl元素以非常规阴离子对或聚阴离子的形式出现,并表现出异于常压和较低压时的化学反应特性.这些特性是否具有普遍性还需要更多的实验体系证实.研究结果为探讨地幔深处氧可能的非常规存在方式提供了新的证据.%In this study we studied the chemical reaction of the NaCl-O 2 system under high pressure and high temperature using the diamond anvil cell apparatus and the double-sided laser heating tech-nology.The sample was heated to about 1500-2000 K under a pressure of 55 GPa,and then analyzed by the Raman measurement at room temperature.The determined data show that the NaCl-O 2 system undergoes a chemical reaction under the above-mentioned pressure and temperature conditions.The products include the nontraditional compounds of NaO4 and NaCl3 ,as well as a small amount of NaClO4 and intermediate product Cl2 .The black NaO4 powder,being apt to absorb moisture,can still exist in the ambient condition.The diagnostic zero-pressure Raman band of 1384 cm-1 ,assigned to the symmetric stretching vibration of the O-4 anion in NaO4 ,suggests the occurrence of O-O atom pair with a negative fractional valence in the structure.The orthorhombic structure of NaCl3 exhibited a strong Raman signal,which could distinguish 10 Raman peaks in our measurements.It decomposes into NaCl+ Cl2 under about 23 GPa on decompression.The experimental results suggest that both elements of oxygen and chlorine prefer to occur in the unconventional form of pair-anions or polyan-ions caused by their unique chemical reactivity under high pressure,differing from that in atmospheric and lower pressure environments.It requires more robust evidences from various experimental sys-tems to confirm whether these properties of oxygen and chlorine under high pressure are universal. Oxygen is one of the most important constituent elements on Earth,and most of the Earth is in high temperature and high pressure environment.This study provides new evidence for the possible uncon-ventional existence of oxygen in the mantle.