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.