Dinu Dennis F, Podewitz Maren, Grothe Hinrich, Loerting Thomas, Liedl Klaus R
Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, A-6020 Innsbruck, Austria.
Institute of Materials Chemistry, TU Wien, A-1060 Vienna, Austria.
Phys Chem Chem Phys. 2020 Aug 24;22(32):17932-17947. doi: 10.1039/d0cp02121k.
Gas-phase IR spectra of carbon dioxide and methane are nowadays well understood, as a consequence of their pivotal roles in atmospheric- and astrochemistry. However, once those molecules are trapped in noble gas matrices, their spectroscopic properties become difficult to conceptualize. Still, such spectra provide valuable insights into the vibrational structure. In this study, we combine new matrix-isolation infrared (MI-IR) spectra at 6 K in argon and neon with in vacuo anharmonic spectra computed by vibrational self-consistent field (VSCF) and vibrational configuration interaction (VCI). The aim is to separate anharmonicity from matrix effects in the mid-infrared spectra of 12C16O2, 12CH4, and 12CD4. The accurate description of anharmonic potential energy surfaces including mode-coupling allows to reproduce gas-phase data with deviations of below 3 cm-1. Consequently, the remaining difference between MI-IR and VSCF/VCI can be attributed to matrix effects. Frequency shifts and splitting patterns turn out to be unsystematic and dependent on the particular combination of analyte and noble gas. While in the case of neon matrices these effects are small, they are pronounced in xenon, krypton, and argon matrices. Our strategy allows us to suggest that methane rotates in neon matrices - in contrast to previous reports.
如今，由于二氧化碳和甲烷在大气化学和天体化学中起着关键作用，它们的气相红外光谱已得到很好的理解。然而，一旦这些分子被困在稀有气体基质中，它们的光谱性质就变得难以概念化。尽管如此，这样的光谱为振动结构提供了有价值的见解。在本研究中，我们将6K下在氩气和氖气中的新的基质隔离红外（MI-IR）光谱与通过振动自洽场（VSCF）和振动组态相互作用（VCI）计算的真空非谐光谱相结合。目的是在12C16O2、12CH4和12CD4的中红外光谱中分离非谐性和基质效应。对包括模式耦合在内的非谐势能面的准确描述能够以低于3cm-1的偏差重现气相数据。因此，MI-IR与VSCF/VCI之间的剩余差异可归因于基质效应。频移和分裂模式被证明是无系统的，并且取决于分析物和稀有气体的特定组合。虽然在氖气基质的情况下这些效应很小，但在氙气、氪气和氩气基质中它们很明显。我们的策略使我们能够提出，与之前的报道相反，甲烷在氖气基质中会旋转。
