High pressure optical cell for synthesis and in situ Raman spectroscopy of hydrogen clathrate hydrates

We report the design, realization, and test of a high-pressure optical cell that we have used to measurethe Raman spectra of hydrogen clathrate hydrates, synthesized in situ by the application of200-300 MPa of gas pressure on solid water. The optical apparatus is mounted on a cryogenic systemso to allow measurements and sample treatment at any temperature between 300 and 20 K. Acapillary pipe is connected to the inside of the cell to allow the gas flow into and out of the cell, andto regulate the internal pressure at any value from 0 to 300 MPa. In the experimental test describedin this paper, the cell has been partly filled, at room temperature, with a small amount of water, thenfrozen at 263 K before injecting hydrogen gas, at pressure of 150 MPa, into the cell. This procedurehas permitted to study hydrogen clathrate formation, by measuring Raman spectra as a function oftime.