LUNAM Université, Université d'Angers, CNRS UMR 6200, Laboratoire MOLTECH-Anjou, 2 Bd Lavoisier, 49045 Angers, France.
J Chem Phys. 2013 May 7;138(17):174308. doi: 10.1063/1.4803160.
The room-temperature isotropic spectrum of SF6 was recorded at the frequency of the 2ν5 overtone by running high-sensitivity incoherent Raman experiments for two independent polarizations of the incident beam and for gas densities varying from 2 to 27 amagat. Weak yet observable pressure effects were found. A transparent analysis of the Raman cross-section problem along with the first-ever prediction of the value of the mean polarizability second derivative ∂(2)α/∂q5(2) are made and the hitherto underestimated role of the hot bands of SF6 is brought to the wider public. The emergence of an analytic hotband factor is shown whose magnitude is dramatically increased with the order of the overtone and the gas temperature and all the more so upon considering low-frequency molecular vibrations. Our formulas, which in the harmonic approximation are exact, are still applicable to real situations provided certain conditions are fulfilled. For nondegenerated modes, generalization to higher order overtones is made, an issue addressing the much challenging problem of the IR-allowed second overtone bands. The content of this paper is also an invitation towards ab initio derivative-calculations for sulfur hexafluoride, especially given the today's needs in interpreting spectra of significance for greenhouse atmospheric issues.
室温各向同性 SF6 的光谱在 2ν5 泛频处被记录下来，通过运行两个独立入射光束偏振方向的高灵敏度非相干拉曼实验，以及气体密度从 2 到 27 大气压变化来实现。结果发现了微弱但可观测的压力效应。对拉曼截面问题进行了透明分析，并首次预测了平均极化率二阶导数 ∂(2)α/∂q5(2) 的值，从而将 SF6 的热带的被低估的作用带给了更广泛的公众。显示出出现了一个解析的热带因子，其大小随着泛频和气体温度的阶数而急剧增加，在考虑低频分子振动时更是如此。我们的公式在简谐近似下是精确的，只要满足某些条件，它们仍然适用于实际情况。对于非简并模式，将其推广到更高阶的泛频，这是一个解决 IR 允许的第二泛频带的更具挑战性问题的问题。本文的内容还邀请对六氟化硫进行从头算导数计算，特别是考虑到当今解释对温室大气问题有重要意义的光谱的需求。
