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Raman signal from a hindered hydrogen rotor

机译：来自阻碍氢转子的拉曼信号

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摘要

We present a method for calculation of Raman modes of the quantum solid phase I hydrogen and deuterium. We use the mean-field assumption [hat 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 ~(2)1/2 as the modes acquire librational character due to stronger interactions. The ratio overshoots ~(2)1/2 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 5_0(0) contributions. The experimental Raman spectrum for phase Ⅱ cannot be reproduced, suggesting that the mean-lield assumption is invalid in that case.
机译：我们提出了一种计算量子固相I氢和氘的拉曼模式的方法。我们使用平均场假设[帽子量化激励在一个分子上定位。这是通过在角度依赖性潜在的时间依赖施罗德格方程的明确解决方案来完成的，并直接计算极化。我们表明，在自由转子极限中，H_2和D_2频率在2倍的倍数下不同，这在由于模式由于更强的交互而获得陈词曲线而发展为〜（2）1/2。如果Anharmonic术语削弱了谐波潜力，则比率过冲〜（2）1/2。我们还使用密度泛函理论和分子动力学来计算E_（2G）光学声子频率和拉曼线宽。分子动力学表明，除了极低的压力和高温下，分子不是自由转子，并且随着Ⅱ阶段接近阶段而变得像振荡器。我们适合对实验频率的相互作用优势，但对强度的良好一致性要求我们还包括S_0（1）和5_0（0）款项之间的强烈的优选方向和刺激的拉曼效应。不能再现Ⅱ阶段的实验拉曼光谱，表明平均Liell假设在这种情况下无效。

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  • 来源
    《Physical review》 |2020年第6期|064102.1-064102.11|共11页
  • 作者

    Peter I. C. Cooke; Ioan B. Magdau; Miriam Pena-Alvarez; Veronika Afonina; Philip Dalladay-Simpson; Xiao-Di Liu; Ross T. Howie; Eugene Gregoryanz; Graeme J. Ackland;

  • 作者单位

    CSEC SUPA School of Physics and Astronomy The University of Edinburgh Edinburgh EH9 3JZ United Kingdom;

    CSEC SUPA School of Physics and Astronomy The University of Edinburgh Edinburgh EH9 3JZ United Kingdom Department of Chemistry and Chemical Engineering Caltech Pasadena California 91125 USA;

    CSEC SUPA School of Physics and Astronomy The University of Edinburgh Edinburgh EH9 3JZ United Kingdom;

    CSEC SUPA School of Physics and Astronomy The University of Edinburgh Edinburgh EH9 3JZ United Kingdom;

    Center for High Pressure Science & Technology Advanced Research Shanghai 201203 People's Republic of China;

    Key Laboratory of Materials Physics Institute of Solid-State Physics HFIPS Chinese Academy of Sciences Hefei 230031 China;

    Center for High Pressure Science & Technology Advanced Research Shanghai 201203 People's Republic of China;

    CSEC SUPA School of Physics and Astronomy The University of Edinburgh Edinburgh EH9 3JZ United Kingdom Center for High Pressure Science & Technology Advanced Research Shanghai 201203 People's Republic of China Key Laboratory of Materials Physics Institute of Solid-State Physics HFIPS Chinese Academy of Sciences Hefei 230031 China;

    CSEC SUPA School of Physics and Astronomy The University of Edinburgh Edinburgh EH9 3JZ United Kingdom;

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