超微扰理论计算双原子分子晶体的拉曼信号
Calculating the Raman Signal Beyond Perturbation Theory for a Diatomic Molecular Crystal
摘要：
我们计算了在一定范围内的模型平均场势的双原子分子的本征态，并评估其相关的拉曼光谱与场强的演变。我们证明，戏剧性的变化，在外观的双原子分子的拉曼光谱发生没有任何相关的变化，周围的潜力的对称性。量子本征态的极限情况对应于经典意义上的自由旋转和定向良好的分子的天平动。然而，也有许多混合模式既不是转子也不是librons。拉曼光谱的结果是一系列的复杂性-非谐波势分裂拉曼活性模式，并打破了禁戒模式的选择规则。各种状态的质量依赖性是不同的-转子，振荡器和重定向分别具有$1/m$，$1/\sqrt{m}$和较弱的质量依赖性。这可以允许人们用同位素光谱学来识别模式的特征。然而，混合模式和两个不同特征的本征态之间的跃迁使其复杂化。我们的结论是，在拉曼光谱的分子系统的显着变化是不够的，以证明一个相变，因为这样的变化也可以发生在一个固定的对称电位时，增加电场强度。
英文摘要：
We calculate the eigenstates of a diatomic molecule in a range of model mean-field potentials, and evaluate the evolution of their associated Raman spectra with field strength. We demonstrate that dramatic changes in the appearance of the Raman spectrum for a diatomic molecule occur without any associated change in the symmetry of the surrounding potential. The limiting cases of the quantum eigenstates correspond, in the classical sense, to free rotation, and libration of well-oriented molecules. However, there are also many mixed modes which are neither rotons nor librons. The consequence for Raman spectroscopy is a series of complications - the non-harmonic potential splits the Raman active modes, and breaks the selection rules on forbidden modes. The mass-dependence of the various states is different - rotors, oscillators and reorientations have $1/m$, $1/\sqrt{m}$ and weaker mass dependence respectively. This may allow one to identify the character of the mode with isotope spectroscopy. However it is complicated by mixed modes and transitions between two different eigenstates with different character. We conclude that significant changes in the Raman spectrum of molecular systems are insufficient to demonstrate a phase transition since such changes can also occur in a fixed symmetry potential upon increasing field strength.
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