Institute of Materials Chemistry , TU Wien , A-1060 Vienna , Austria.
J Phys Chem A. 2019 Sep 26;123(38):8234-8242. doi: 10.1021/acs.jpca.9b07221. Epub 2019 Sep 12.
Rotational-vibrational spectroscopy of water in solid noble gas matrices has been studied for many decades. Despite that, discrepancies persist in the literature about the assignment of specific bands. We tackle the involved rotational-vibrational spectrum of the water isotopologues HO, HDO, and DO with an unprecedented combination of experimental high-resolution matrix isolation infrared (MI-IR) spectroscopy and computational anharmonic vibrational spectroscopy by vibrational configuration interaction (VCI) on high-level ab initio potential energy surfaces. With VCI, the average deviation to gas-phase experiments is reduced from >100 to ≈1 cm when compared to harmonic vibrational spectra. Discrepancies between MI-IR and VCI spectra are identified as matrix effects rather than missing anharmonicity in the theoretical approach. Matrix effects are small in Ne (≈1.5 cm) and a bit larger in Ar (≈10 cm). Controversial assignments in Ne MI-IR spectra are resolved, for example, concerning the ν triad in HDO. We identify new transitions, for example, the ν 1 ← 1 transition in DO and HO or the ν 0 ← 1 transition in DO, and reassign bands, for example, the band at 3718.9 cm that is newly assigned as the 1 ← 1 transition. The identification and solution of discrepancies for a well-studied benchmark system such as water prove the importance of an iterative and one-hand combination of theory and experiment in the field of high-resolution infrared spectroscopy of single molecules. As the computational costs involved in the VCI approach are reasonably low, such combined experimental/theoretical studies can be extended to molecules larger than triatomics.
几十年来，人们一直在研究水在固体惰性气体基质中的转动-振动光谱。尽管如此，关于特定谱带的分配，文献中仍然存在差异。我们采用前所未有的实验高分辨率基质隔离红外（MI-IR）光谱和基于振动构型相互作用（VCI）的计算非谐振动光谱相结合的方法，研究了水同位素 HO、HDO 和 DO 的复杂转动-振动光谱。通过 VCI，与谐振动光谱相比，与气相实验的平均偏差从>100 cm减小到≈1 cm。MI-IR 和 VCI 光谱之间的差异被确定为基质效应，而不是理论方法中缺少非谐性。在 Ne（≈1.5 cm）中基质效应较小，在 Ar 中稍大（≈10 cm）。解决了 Ne MI-IR 光谱中的一些有争议的分配问题，例如 HDO 中的 ν 三重态。我们鉴定了一些新的跃迁，例如 DO 和 HO 中的 ν 1 ← 1 跃迁，或者 DO 中的 ν 0 ← 1 跃迁，并重新分配了一些谱带，例如 3718.9 cm 处的谱带，它被重新分配为 1 ← 1 跃迁。对于水这样一个经过充分研究的基准体系，差异的识别和解决证明了在单分子高分辨率红外光谱领域中，理论和实验的迭代和一手结合的重要性。由于 VCI 方法涉及的计算成本相对较低，因此可以将这种组合的实验/理论研究扩展到比三原子分子更大的分子。
