Effect of guest–host interaction on Raman spectrum of a CO2 clathrate hydrate single crystal

Abstract

The polarized Raman spectra of an artificial CO2 clathrate hydrate single crystal have been measured in order to examine the crystal-orientation dependence of the Raman spectra. Since the crystal had crystallographic facets, the orientation of the crystal was determined by using the Miller indices of the facets. When the angle θ between the polarization plane of the incident laser beam and the direction of one of the 〈110〉 axes of the single crystal varied, it was observed that the intensities of the peaks, which were caused by the Fermi resonance of the symmetric stretching mode and the overtone of the bending mode of CO2, and the O–H symmetric stretching vibration mode, varied with θ. Since the tetrakaidecahedron cage in the CO2 clathrate hydrate is distorted along the 〈100〉 axis, the variations of the scattering intensities of the CO2 have been calculated by using a simple model that assumes that the CO2 rotates on the {100} plane in the tetrakaidecahedron cage. The results obtained from the experiments are consistent with the calculations made by using this model. It has been concluded that the anisotropy of the peak intensities of the CO2 show the influence of the cage geometry on the motion of the guest molecule. The anisotropy of the O–H symmetric stretching vibration mode was interpreted with a five-body structure model. As the calculation with the model was consistent with the result obtained from the experiment, it was found that the anisotropy of the peak intensity of the O–H symmetric stretching vibration mode was related to the arrangement of the water molecules. We consider that the result indicates the influence of the motion of the guest molecule on the surrounding hydrogen-bonded network.

Formation, growth and ageing of clathrate hydrate crystals in a porous medium

“…Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. In a system consisting of liquid water and a guest fluid that is sparingly soluble in water, it is generally accepted that an interface between the guest fluid and the liquid water is the preferential nucleation site for hydrates [1][2][3][4][5][6][7][8]. In addition, recent studies [1][2][3][4][5][6][7][8][9][10] have revealed that hydrate crystals grow into liquid water, if the liquid water has dissolved the guest substance up to saturation prior to hydrate formation.…”

“…In a system consisting of liquid water and a guest fluid that is sparingly soluble in water, it is generally accepted that an interface between the guest fluid and the liquid water is the preferential nucleation site for hydrates [1][2][3][4][5][6][7][8]. In addition, recent studies [1][2][3][4][5][6][7][8][9][10] have revealed that hydrate crystals grow into liquid water, if the liquid water has dissolved the guest substance up to saturation prior to hydrate formation. Visual information available for hydrate formation, growth, and ageing in fourphase systems, consisting of guest substance þ hydrate þ liquid water þ sediments, is limited to the observations of Tohidi et al [9,10], whereas studies of simple threephase systems consisting of guest substance þ hydrate þ liquid water are abundant [1][2][3][4][5][6][7][8].…”

“…In addition, recent studies [1][2][3][4][5][6][7][8][9][10] have revealed that hydrate crystals grow into liquid water, if the liquid water has dissolved the guest substance up to saturation prior to hydrate formation. Visual information available for hydrate formation, growth, and ageing in fourphase systems, consisting of guest substance þ hydrate þ liquid water þ sediments, is limited to the observations of Tohidi et al [9,10], whereas studies of simple threephase systems consisting of guest substance þ hydrate þ liquid water are abundant [1][2][3][4][5][6][7][8]. The studies by Tohidi et al [9,10] were carried out in the pore space of a glass micromodel, a semi-two-dimensional glass mimic of sediments consisting of an etched glass plate and a cover glass plate.…”

Diffusion of nitrogen gas in ice Ih

“…The vibrational motion of N 2 in ice lattice is expected to govern the diffusion mechanism. The vibrational motion of linear molecules such as N 2 distorts the structure of ice lattice [12,13]. Using neutron scattering, Ikeda et al [14][15][16] confirmed that the rotational and translational motions of the linear molecule have strong influence on the dynamics of the surrounding hydrogen-bonded network.…”

Characterization of Salting-Out Processes during CO2-Clathrate Formation Using Raman Spectroscopy: Planetological Application

“…The close Raman shift in both states suggests that the reorganization of H 2 O molecules around the CO 2 molecule is quite similar, signifying the existence of clathrate-like structures in the liquid state. [15,16] When salts are present in the solution, the high affinity between water molecules and the electrolytes promotes two processes that drive a decrease in the clathrate equilibrium temperature: (1) the reduction in the gas solubility and (2) the difficulty of the reorganization of the H 2 O molecules in the clathrate cage; salts do not take part of the solid structure. This is the so-called ''salting-out'' effect that we monitored by Raman spectroscopy.…”