Raman spectra of natural clathrates in deep ice cores

Abstract

Raman spectra of natural clathrates at a depth of 1501 m in ice cores collected at Dye-3 (Greenland) have been measured from 10 to 3500 cm⁻¹. The guest molecules in the clathrates were identified as O₂ and N₂ from their molecular vibrations. The energy shifts of the vibrational modes have been analysed by a simple model of a spherical cavity in a dielectric medium. From a comparison of calculations with observations, it is concluded that guest molecules occur only in the larger cages of the clathrates. Temperature-dependent Raman spectra have been measured from 10 to 100 cm⁻¹. The peak position shifts to a lower Raman shift at lower temperatures. This structure is considered to arise from over-damping of the rotation modes of the guest molecules.