Modulated structure of solid iodine during its molecular dissociation under high pressure
Modulated structure of solid iodine during its molecular dissociation under high pressure
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DOI：
10.1038/nature01724
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发表时间：
2003-06-26
期刊：
影响因子：
64.8
通讯作者：
Mitsuko, O
中科院分区：
文献类型：
--
作者：
Kenichi, T;Kyoko, S;Mitsuko, O
对固体碘施加压力迫使晶体中的分子相互靠近，直到分子间的距离与碘的键长相当；在这一点上，分子失去了身份，基本上解离了。根据室温X射线衍射研究(1)，这一过程涉及到约21 Gpa的碘分子的直接解离，而光谱观察(2，3)在15至30 Gpa的压力范围内发现了中间分子相。在这里，我们提出了准静压粉末X射线衍射测量，清楚地揭示了在压力诱导的固体碘解离过程中的中间相。我们发现，与铀(4)的行为类似，这个中间相的结构是无公度调制的，最近的原子间距离连续分布在2.86-3.11埃的范围内。最短的原子间距离介于分子晶体中碘的键长(2.75埃)和完全解离的单原子晶体中最近的原子间距离(2.89埃)之间，这意味着中间相在分子解离过程中是一个暂态。我们期望在不同温度下的进一步测量将有助于阐明无公度结构的起源和稳定性，这可能有助于更好地理解在这里以及氢(5)、氧(6)和氮(7)的分子晶体中看到的压力诱导解离的分子水平机制。
The application of pressure to solid iodine forces the molecules in the crystal to approach each other until intermolecular distances become comparable to the bond length of iodine; at this point, the molecules lose their identity and are essentially dissociated. According to room-temperature X-ray diffraction studies(1), this process involves direct dissociation of iodine molecules at about 21 GPa, whereas spectroscopic observations(2,3) have identified intermediate molecular phases at pressures ranging from 15 to 30 GPa. Here we present quasi-hydrostatic powder X-ray diffraction measurements that clearly reveal an intermediate phase during the pressure-induced dissociation of solid iodine. We find that, similar to the behaviour seen in uranium(4), the structure of this intermediate phase is incommensurately modulated, with the nearest interatomic distances continuously distributed over the range 2.86 - 3.11 Angstrom. The shortest of these interatomic distances falls between the bond length of iodine in the molecular crystal (2.75 Angstrom) and the nearest interatomic distance in the fully dissociated monatomic crystal (2.89 Angstrom), implying that the intermediate phase is a transient state during molecular dissociation. We expect that further measurements at different temperatures will help to elucidate the origin and stability of the incommensurate structure, which might lead to a better understanding of the molecular-level mechanism of the pressure-induced dissociation seen here and in the molecular crystals of hydrogen(5), oxygen(6) and nitrogen(7).