LUNAM Université, Université d'Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 Bd Lavoisier, 49045 Angers, France.
J Chem Phys. 2014 Mar 28;140(12):124308. doi: 10.1063/1.4869097.
Of the six normal vibrations of SF6, ν3 has a key role in the mechanisms of radiative forcing. This vibration, though inactive in Raman, shows up through the transition 2ν3 allowing for a complementary view on the asymmetric stretch of the molecule. Here, we look back into this topic, which has already caught some interest in the past but with some points been left out. We make a systematic incoherent-light-scattering analysis of the overtone with the use of different gas pressures and polarization orientations for the incident beam. Absolute-scale isotropic and anisotropic spectra are reported along with natural and pressure-induced widths and shifts, and other spectral features such as the peaks corresponding to the (experimentally indistinguishable) interfering channels Eg and F2g hitherto seen solely as two-photon IR-absorption features. We make the first-ever prediction of the SF6 polarizability second derivative with respect to the ν3-mode coordinate and we develop a heuristic argument to explain why the superposition of the three degenerate stretching motions that are related to the ν3 mode cannot but generate a polarized Raman band.
SF6 的六种正则振动中，ν3 在辐射强迫机制中起着关键作用。这种振动虽然在拉曼中不活跃，但通过跃迁 2ν3 表现出来，从而可以对分子的不对称伸缩提供一个补充的视角。在这里，我们回顾一下这个话题，它在过去已经引起了一些关注，但有些方面被忽略了。我们使用不同的气体压力和入射光束的偏振方向，对泛音进行了系统的非相干光散射分析。报告了各向同性和各向异性的绝对谱以及自然和压力诱导的宽度和位移，以及其他光谱特征，如对应于（实验上不可区分的）干涉通道 Eg 和 F2g 的峰，这些峰迄今仅被视为双光子红外吸收特征。我们首次预测了 SF6 极化率相对于 ν3 模式坐标的二阶导数，并提出了一个启发式论点来解释为什么与 ν3 模式相关的三个简并伸缩运动的叠加必然会产生极化拉曼带。
