水對於地球內部的物理與化學性質有著極大的影響。本文的主題所提到的Phase A是重水鎂矽酸鹽類的一種，所代表的地質意義是在板塊下插的過程中，橄欖岩質的板塊會因為水及壓力的作用，生成蛇紋岩。蛇紋岩在更高的壓力作用下會轉換成另一種含水礦物，即是我們所談論的Phase A。(Ulmer and Trommsdorff, 1995)
　　本文的實驗是在美國的國家布魯克海文實驗室中的同步幅射光源所進行的。本次實驗利用高壓鑽石鉆，將樣品由常溫常壓的狀態下，加壓至32 GPa的高壓狀態；並在各個適當的壓力點，收取其紅光外吸收譜。
　　結果，我們發現在晶格的振動模中，它們會隨著壓力的增加，往高頻的方向移動。但是，在OH的伸張模中(3410.9 cm-1 and 3517 cm-1)，我們卻看到它們隨著壓力的增加，頻率卻呈線性狀的遞減，而且在13 GPa時，兩者的差異達到最小。超過13 GPa後，兩個伸張模的斜率產生改變，在晶格震動模中，似乎也可觀察到類似現象。這個現象大概指向兩種可能，可能是微結構上的改變，或是只為單純的壓縮機制所造成的。類似的結果亦可在拉曼實驗(Liu et al. 1997)中觀察到。在前人的研究中，他們也觀察到類似的結果，不同的是，他們所觀察到的轉折點是在18 GPa，並且在18 GPa後，他們觀察到了一根新生的OH伸張模出現。本次實驗與前人研究兩者之間的差異處(壓力轉折點的不同以及新生的OH伸張模)，則需要更深入的研究與實驗來進行討論。

Water has great influences on the physical properties and chemical reactions of the mantle phases. Phase A is one of the dense hydrous magnesium silicates fromed in the high pressure environment. Structurally and chemically Phase A has been suggested to be related to the serpentine mineral, antigorite in the subduction slabs (Ulmer and Trommsdorff, 1995).
High pressure infrared experiments were carried at beamline U2A, National Synchrotron Light Source. The absorption spectra were collected up to 32 GPa at the ambient temperatures. The wavenumbers (ω) of the lattice vibration modes increase progressively as a function of pressure, but those of the OH bands (3410.9 cm-1 and 3517 cm-1) were decreasing linearly. The slopes (∂ω/∂P) of lattice vibration modes and the OH modes change at pressure of 13 GPa. For the OH modes, the ∆ω (wavenumber difference, ω3517 cm-1 – ω3410.9 cm-1) decreased gradually during the compression and had a minima value at 13 GPa. Above 13 GPa, the ∆ω increases with increasing pressure. All these changes may be taken as evidence for a minor structure change or a compression mechanism in Phase A at pressure greater than 13 GPa. A similar phenomenon was also observed in a previous Raman study (Liu et al. 1997), that the transition pressure was reported to occur above 18 GPa. Furthermore, we did not observe the splitting of the most intense OH band (3517 cm-1), which was reported by Liu et al. (1997). These discrepancies need to be further investigated.

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