受阻转子的扰动信号
The raman signal of a hindered rotor
摘要：
本文提出了一种计算量子固相Ⅰ固体氢和氘的喇曼模的方法。我们使用的平均场假设的量子化激发是本地化的一个分子。这是通过显式解的时间依赖薛定谔方程在一个角度依赖的潜力，并直接计算的极化。我们表明，在自由转子的限制，H $_2$和D $_2$频率不同的2个因素，这朝着$\sqrt{2}$的模式获得librational字符由于更强的相互作用。如果非调和项削弱了调和势，则比值超过$\sqrt{2}$。我们还利用密度泛函理论和分子动力学方法计算了E $_{2_g}$光学声子频率和拉曼谱线宽度。分子动力学表明，分子除了在极低的压力和高温下不是自由转子，并在接近第II相时变成类似于振子。我们将相互作用强度与实验频率进行了拟合，但强度的良好一致性要求我们还包括S $_0$（1）和S $_0$（0）贡献之间的强择优取向和受激拉曼效应。第二阶段的实验拉曼光谱无法再现，表明在这种情况下，平均场假设是无效的。
英文摘要：
We present a method for calculation of Raman modes of the quantum solid phase I solid hydrogen and deuterium. We use the mean-field assumption that the quantised excitations are localized on one molecule. This is done by explicit solution of the time-dependent Schroedinger equation in an angle-dependent potential, and direct calculation of the polarisation. We show that in the free-rotor limit, the H$_2$ and D$_2$ frequencies differ by a factor of 2, which evolves toward $\sqrt{2}$ as the modes acquire librational character due to stronger interactions. The ratio overshoots $\sqrt{2}$ if anharmonic terms weaken the harmonic potential. We also use density functional theory and molecular dynamics to calculate the E$_{2_g}$ optical phonon frequency and the Raman linewidths. The molecular dynamics shows that the molecules are not free rotors except at very low pressure and high temperature, and become like oscillators as phase II is approached. We fit the interaction strengths to experimental frequencies, but good agreement for intensities requires us to also include strong preferred-orientation and stimulated Raman effects between S$_0$(1) and S$_0$(0) contributions. The experimental Raman spectrum for phase II cannot be reproduced, showing that the mean-field assumption is invalid in that case.
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