Mollica Nardo Viviana, Cassone Giuseppe, Ponterio Rosina Celeste, Saija Franz, Sponer Jiri, Tommasini Matteo, Trusso Sebastiano
IPCF-CNR, Istituto per i Processi Chimico-Fisici, Viale F. Stagno d'Alcontres 37, 98158 Messina, Italy.
Institute of Biophysics of the Czech Academy of Sciences, Královopolská 135, 61265 Brno, Czech Republic.
J Phys Chem A. 2020 Dec 24;124(51):10856-10869. doi: 10.1021/acs.jpca.0c09791. Epub 2020 Dec 11.
Intense static electric fields can strongly perturb chemical bonds and induce frequency shifts of the molecular vibrations in the so-called vibrational Stark effect. Based on a density functional theory (DFT) approach, here, we report a detailed investigation of the influence of oriented external electric fields (OEEFs) on the dipole moment and infrared (IR) spectrum of the nonpolar centrosymmetric indigo molecule. When an OEEF as intense as ∼0.1 V Å is applied, several modifications in the IR spectrum are observed. Besides the notable frequency shift of some modes, we observe the onset of new bands-forbidden by the selection rules in the zero-field case. Such a neat field-induced modification of the vibrational selection rules, and the subsequent variations of the peaks' intensities in the IR spectrum, paves the way toward the design of smart tools employing centrosymmetric molecules as proxies for mapping local electric fields. In fact, here, we show that the ratio between the IR and the Raman intensities of selected modes is proportional to the square of the local field. This indicator can be used to quantitatively measure local fields, not only in condensed matter systems under standard conditions but also in field-emitting-tip apparatus.
强静电场会强烈扰动化学键，并在所谓的振动斯塔克效应中引起分子振动的频率偏移。基于密度泛函理论（DFT）方法，在此我们报告了关于定向外部电场（OEEF）对非极性中心对称靛蓝分子的偶极矩和红外（IR）光谱影响的详细研究。当施加强度约为0.1 V Å的OEEF时，在IR光谱中观察到了一些变化。除了某些模式明显的频率偏移外，我们还观察到了新谱带的出现——这些谱带在零场情况下是被选择定则禁止的。这种由场诱导的振动选择定则的清晰变化，以及随后IR光谱中峰强度的变化，为设计以中心对称分子作为映射局部电场替代物的智能工具铺平了道路。事实上，在此我们表明，所选模式的IR强度与拉曼强度之比与局部场的平方成正比。该指标不仅可用于定量测量标准条件下凝聚态物质系统中的局部场，还可用于场发射尖端装置中的局部场测量。
