Abstract

Mid-infrared spectra of difluoromethane (DFM) have been recorded by confining the molecule in the matrix cages of pure argon, nitrogen and in the mixed matrixes of argon and nitrogen obtained by mixing the two gases in definite proportions. The measured spectra depict distinct confinement effects in terms of the infrared spectral shifts of the C–H and C–F stretching vibrational fundamentals as compared to the free molecules in the gas-phase, and also some remarkable changes in band appearances and relative intensities. The signs of the spectral shifts are observed to be different for the \(\upnu _{\text {C--H}}\) and \(\upnu _{\text {C--F}}\) transitions. Pronounced blue shifts are observed for the two \(\upnu _{\text {C--H}}\) modes in pure nitrogen matrix, which progressively reduce in magnitude in the mixed matrixes, and is least in the pure argon matrix. On the other hand, distinct red shifts of the \(\upnu _{\text {C--F}}\) vibrations are evident in pure nitrogen matrix, which are reduced in magnitude in the mixed matrixes, and become even less pronounced in pure argon matrix. The effect of Fermi resonances in the \(\upnu _{\text {C--H}}\) region, that has motivated several previous investigations of DFM including high resolution gas phase studies, becomes explicit upon comparison of the matrix isolation spectrum with the gas phase spectrum. Electronic structure calculations using several DFT and DFT-D methods, in conjunction with NBO analysis, have been carried out for various sizes of \(\hbox {DFM-N}_{2}\) and DFM-Ar complexes in order to understand the underlying interactions responsible for the observed shifts. The calculations are found to satisfactorily reproduce the observed variations in magnitude and direction of the shifts of both the \(\upnu _{\text {C--H}}\) and \(\upnu _{\text {C--F}}\) transitions for the change of the medium. It is inferred that the inert gas matrix environment exerts an electronic re-organization within the DFM molecule, and the consequent rehybridization of the carbon-centric hybrid orbital of the C–H and C–F bonds is responsible for the observed spectral shifts.

Graphic abstract

中文翻译：

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限制对冷惰性气体基质中二氟甲烷的CH和CH伸缩振动频率的影响：红外光谱和电子结构理论的结合

摘要

通过将分子限制在纯氩气，氮气的骨架笼子中以及将两种气体按一定比例混合而获得的氩气和氮气的混合基质中，记录了二氟甲烷（DFM）的中红外光谱。与气相中的游离分子相比，测得的光谱根据C–H和C–F拉伸振动基波的红外光谱位移描绘了明显的限制效应，并且在谱带外观和相对强度方面也发生了一些显着变化。对于\（\ upnu _ {\文本{C–H}} \）和\（\ upnu _ {\文本{C–F}} \）跃迁，观察到光谱位移的符号是不同的。对于两个\（\ upnu _ {\ text {C--H}} \），观察到明显的蓝移纯氮基体中的模态，其在混合基体中的大小逐渐减小，而在纯氩基体中最小。另一方面，\（\ upnu _ {\ text {C–F}} \）振动的明显红移在纯氮基体中很明显，在混合基体中幅度减小，甚至变得不那么明显。在纯氩气基质中。通过比较基质分离谱，可以清楚地了解\（\ upnu _ {\ text {C--H}} \）区域中费米共振的影响，该影响促使了先前的DFM研究，包括高分辨率气相研究。气相色谱 已针对多种尺寸的金属进行了几种DFT和DFT-D方法的电子结构计算，并结合NBO分析进行了计算。\（\ hbox {DFM-N} _ {2} \）和DFM-Ar复合体，以便了解导致观察到的移位的潜在交互作用。发现这些计算可以令人满意地重现\（\ upnu _ {\ text {C--H}} \）和\（\ upnu _ {\ text {C-- F}} \）转换为更改媒体。可以推断，惰性气体基质环境在DFM分子内产生了电子重组，并且随之而来的C–H和C–F键的以碳为中心的杂化轨道的再杂化是观察到的光谱偏移的原因。

图形摘要