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(a) Representative Raman spectra showing the diamond Raman edge on compression of H2 to 318 GPa, frequencies of the stressed edge are indicated. (b) Representative Raman spectra showing the diamond Raman edge (at ∼1760 cm−1) upon a cooling cycle of D2.
Upper panels: D2 and H2 vibron frequency versus diamond Raman edge frequency for several separate experimental runs from this study. The data of the runs where the temperature of the D2 and H2 samples was changed (either cooled or warmed) and then brought back to 300 K are shown in solid black triangles.Lower panels: Vibron frequency versus pressure comparison between this study, Refs. 7 and 29 for deuterium (left panel) and hydrogen (right panel). Solid blue symbols are the frequencies of the vibrons measured in this study versus pressure in GPa; open red triangles are from Ref. 7 and black squares are from Ref. 29 . In all three studies the pressure calibration by Akahama et al. 28 was used. The black solid curves are the polynomial fits to the experimental data.The polynomial forhydrogen vibron frequency as function of pressure is given by 4162 + 9.86246 P-0.396212P2 + 0.00868361P3-0.000113189P4 + 8.42353×10−7P5-3.47943×10−9P6 + 7.37257×10−12P7-6.2332×10−15P8 and for deuterium by 2993 + 8.00349 P-0.30972P2 + 0.0066976P3-8.56127×10−5 P4 + 6.30364×10−7P5-2.60108×10−9P6 + 5.5378×10−12P7-4.71153×10−15P8, where P is pressure in GPa from ambient up to 318 GPa for hydrogen and 270 GPa for deuterium (see text).
Sketches and microphotographs of the sample chamber and the sample. Left Panel (a,c): Scaled sketches of the sample chamber geometry changes under pressure. Note that the thickness of the gasket is known (was measured optically and by the focused ion beam imaging) only before loading; the thickness at given pressures (100, 240, and 280 GPa) is an assumption based on our experience. Right panel (b,d): Microphotographs showing how the sample chamber was observed to partially collapse resulting in a thin layer of hydrogen lying above the gasket material, resulting in partial losses of hydrogen. The dark area are around the sample chamber seen in (b) and (d) is rhenium hydride.
Representative Raman spectra of H2 (bottom) and D2 (top) at diamond edge frequencies of 1765 cm−1 and 1770 cm−1, respectively. The upper spectrum in each isotope shows measurements on the transparent part of the sample (point A, photomicrograph is not shown for D2). The lower (weaker signal) spectrum is a measurement on the partially collapsed part (point B) of the sample chamber as illustrated in the photomicrograph inset. The inset shows a microphotograph in both transmitted and reflected light while the probing laser diffuses on the partially collapsed gasket segment of the hydrogen sample.
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