在室温条件下, 利用金刚石对顶砧超高压技术, 对氨的半水合物(2NH3·H2O) 进行了原位高压拉曼光谱研究, 采用红宝石荧光压标测压, 实验的最高压力为41.0 GPa。装入金刚石对顶砧样品腔的初始样品为液态的氨的半水合物, 当压力达到3.5 GPa时, 显微镜下观察到整个样品腔内均匀的出现块状晶体, 同时, 测量到的拉曼谱上出现许多新的拉曼峰。因此, 我们判断在此压力下液态的2NH3·H2O发生了液固相变。当压力增加到19.0 GPa左右时, 2NH3·H2O的拉曼频移随压力变化的曲线有拐点, 并且具有软化特性的N-H伸缩振动模式消失。我们分析这是因为在高压下, 通过O-H…N成键的II型氨分子发生了旋转, 所以2NH3·H2O在此压力下发生了一次固固相变。

High pressure Raman scattering studies have been performed on liquid ammonia hemihydrates (2NH3·H2O) at room temperature up to 41.0 GPa. The results demonstrate that liquid 2NH3·H2O transforms to a solid phase at 3.5 GPa, evidenced by an abrupt discontinuity of the intramolecular vibration frequencies. Upon increasing pressure, a solid-solid phase transition is observed at about 19.0 GPa. This phase transition originates from the rotation of type II ammonia molecule via the O-H…N bond. High pressure Raman scattering results of 2NH3·H2O provide significant information for understanding the physics of the large icy bodies in the solar system.