氮气、氧气和空气水合物的合成及其拉曼光谱特征

在-20℃和不同的压力下,在实验室内分别合成了氮气水合物(16MPa)、氧气水合物(13MPa)和空气水合物(15MPa),并对其N—N和O—O键伸缩振动的拉曼光谱特征进行了研究。结果表明,人工合成的水合物中的N—N和O—O键的拉曼位移与天然的空气水合物中的数据十分接近。在氮气水合物和空气水合物中,N—N键的拉曼峰值均为2322.4cm-1;O—O键的拉曼峰值在氧气水合物和空气水合物保持一致,均为1547.8cm-1。空气水合物分解的拉曼谱图表明,它不是氮气水合物和氧气水合物组成的混合物,而是由氮分子和氧分子共同生成的单一水合物,氮分子和氧分子同时进入水合物的大笼和小笼中。与空气中的氮、氧比例相比,水合物中氧分子明显富集,氮分子和氧分子的比例为2.4∶1。

Formation and Raman Spectroscopic Characteristics of Nitrogen, Oxygen and Air Hydrates

The nitrogen hydrate,oxygen hydrate and air hydrate samples were synthesized at 16 MPa,13 MPa and 15 MPa,respectively,at-20 ℃ in laboratory.The Laser Raman spectroscopy was used to investigate the characteristics of N—N and O—O stretching vibration in these samples.The results show that Raman shifts of N—N and O—O in the synthesized samples are very similar to those in natural samples.The Raman peak of N2 is observed at 2,322.4 cm-1 both in nitrogen hydrate and in air hydrate,while the Raman peak of O2 at 1,547.8 cm-1 in oxygen hydrate and air hydrate.The Raman spectroscopic observations on air hydrate dissociation suggest that air hydrate is a unit clathrate with N2 and O2 as guest molecules,rather than mixture of pure nitrogen hydrate and oxygen hydrate.The N2 and O2 molecules seem to occupy both the large and small cages of air hydrate together.Compared with the N/O ratio in air,O2 molecule is significantly enriched in the synthesized air hydrate with N2/O2 ratio of 2.4∶1.