Quantum effects of translational motions in solid para-hydrogen and ortho-deuterium: anharmonic extension of the Einstein model
Quantum effects of translational motions in solid para-hydrogen and ortho-deuterium: anharmonic extension of the Einstein model
复制标题
固体仲氢和正氘中平移运动的量子效应：爱因斯坦模型的非调和扩展
DOI：
--
复制
发表时间：
2010
期刊：
影响因子：
--
通讯作者：
A. Schild
中科院分区：
文献类型：
--
作者：
O. Kühn;J. Manz;A. Schild
为了描述零温度极限下平移零点运动对对位 H2 和邻位 D2 晶体的结构和热力学性质的影响，开发了爱因斯坦模型的非谐扩展。因此，分子在其基质笼中进行大幅平移运动，基质笼是由所有其他分子的冻结环境形成的。这些转换从分子平衡位置通过谐波引导至势能表面的非谐波域。由此产生的平移分布大致为各向同性，并且具有近似高斯形状，半峰全宽相当宽，FWHM(para-H2/ortho-D2) = 1.36/1.02 Å。平移零点能量引起晶体膨胀，与实验结果几乎定量一致。此外，它们对升华能和零压力体积模量做出了重大贡献。这些量子效应随着分子质量的增加而减弱。通过将该模型应用于 Ar 晶体，证实了邻位 D2 与对位 H2 的相应同位素效应。这些结果意味着掺杂剂与其主体晶体的激光诱导反应动力学的后果。
An anharmonic extension of the Einstein model is developed in order to describe the effect of translational zero point motion on structural and thermodynamic properties of para-H2 and ortho-D2 crystals in the zero temperature limit. Accordingly, the molecules carry out large amplitude translational motions in their matrix cage, which are formed by the frozen environment of all other molecules. These translations lead from the molecular equilibrium positions via the harmonic to the anharmonic domain of the potential energy surface. The resulting translational distributions are roughly isotropic, and they have approximately Gaussian shapes, with rather broad full widths at half-maximum, FWHM(para-H2/ortho-D2) = 1.36/1.02 Å. The translational zero point energies induce expansions of the crystals, in nearly quantitative agreement with experimental results. Furthermore, they make significant contributions to the sublimation energies and zero pressure bulk moduli. These quantum effects decrease with heavier molecular masses. The corresponding isotope effects for ortho-D2 compared to para-H2 are confirmed by application of the model to Ar crystals. The results imply consequences for laser induced reaction dynamics of dopants with their host crystals.