Raman signal from a hindered hydrogen rotor
Raman signal from a hindered hydrogen rotor
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来自受阻氢转子的拉曼信号
DOI：
10.1103/physrevb.102.064102
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发表时间：
2020-08-05
影响因子：
3.7
通讯作者：
Ackland, Graeme J.
中科院分区：
文献类型：
--
作者：
Cooke, Peter I. C.;Magdau, Ioan B.;Ackland, Graeme J.
本文提出了一种计算量子固相Ⅰ氢和氘的拉曼模的方法。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相关的薛定谔方程在一个角度相关的潜力，并直接计算的极化。我们发现，在自由转子的限制，H-2和D-2频率不同的2倍，这朝着根2的模式获得librational字符由于更强的相互作用的演变。如果非调和项削弱了调和势，则该比值超过根2。我们还利用密度泛函理论和分子动力学方法计算了E-2g光学声子频率和拉曼谱线宽度。分子动力学表明，分子除了在很低的压力和高温下不是自由转子，并成为类似的振荡器相II。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，这表明在这种情况下，平均场假设是无效的。
We present a method for calculation of Raman modes of the quantum solid phase I hydrogen and deuterium. We use the mean-field assumption that the quantized 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 polarization. We show that in the free rotor limit, the H-2 and D-2 frequencies differ by a factor of 2, which evolves toward root 2 as the modes acquire librational character due to stronger interactions. The ratio overshoots root 2 if anharmonic terms weaken the harmonic potential. We also use density functional theory and molecular dynamics to calculate the E-2g 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, suggesting that the mean-field assumption is invalid in that case.