Department of Chemistry & Biochemistry, University of Mississippi, University, MS 38677, USA.
Department of Earth and Environmental Sciences, University of Pennsylvania, Philadelphia, PA 19104, USA.
Molecules. 2022 May 17;27(10):3200. doi: 10.3390/molecules27103200.
For decades, sulfur has remained underdetected in molecular form within the dense interstellar medium (ISM), and somewhere a molecular sulfur sink exists where it may be hiding. With the discovery of hydrogen peroxide (HOOH) in the ISM in 2011, a natural starting point may be found in sulfur-bearing analogs that are chemically similar to HOOH: hydrogen thioperoxide (HOSH) and hydrogen persulfide (HSSH). The present theoretical study couples the accuracy in the anharmonic fundamental vibrational frequencies from the explicitly correlated coupled cluster theory with the accurate rotational constants provided by canonical high-level coupled cluster theory to produce rovibrational spectra for use in the potential observation of HOSH and HSSH. The ν6 mode for HSSH at 886.1 cm-1 is within 0.2 cm-1 of the gas-phase experiment, and the B0 rotational constant for HSSH of 6979.5 MHz is within 9.0 MHz of the experimental benchmarks, implying that the unknown spectral features (such as the first overtones and combination bands) provided herein are similarly accurate. Notably, a previous experimentally-attributed 2ν1 mode, at 7041.8 cm-1, has been reassigned to the ν1+ν5 combination band based on the present work's ν1+ν5 value at 7034.3 cm-1. The most intense vibrational transitions for each molecule are the torsions, with HOSH having a more intense transition of 72 km/mol compared to HSSH's intensity of 14 km/mol. Furthermore, HOSH has a larger net dipole moment of 1.60 D compared to HSSH's 1.15 D. While HOSH may be the more likely candidate of the two for possible astronomical observation via vibrational spectroscopy due to the notable difference in their intensities, both HSSH and HOSH have large enough net dipole moments to be detectable by rotational spectroscopy to discover the role these molecules may have as possible molecular sulfur sinks in the dense ISM.
几十年来，在密集的星际介质（ISM）中，硫一直以分子形式被未被检测到，而且在某个地方存在一个分子硫汇，硫可能隐藏在那里。2011 年，在 ISM 中发现了过氧化氢（HOOH），因此在与 HOOH 在化学上相似的含硫类似物中可能会发现一个自然的起点：氢过硫醚（HOSH）和氢过二硫酸盐（HSSH）。本理论研究将从明确相关耦合簇理论中获得的精确非谐基本振动频率与正则高级耦合簇理论提供的精确旋转常数相结合，为 HOSH 和 HSSH 的潜在观测产生转动-振动光谱。HSSH 的ν6 模式在 886.1cm-1 处，与气相实验值相差 0.2cm-1，HSSH 的 B0 旋转常数为 6979.5MHz，与实验基准值相差 9.0MHz，这意味着本文提供的未知光谱特征（如第一泛音和组合带）同样准确。值得注意的是，以前实验归因于 7041.8cm-1 的 2ν1 模式，根据本工作的ν1+ν5 值 7034.3cm-1，已被重新分配到ν1+ν5 组合带。每个分子最强烈的振动跃迁是扭转，HOSH 的跃迁强度为 72km/mol，而 HSSH 的跃迁强度为 14km/mol。此外，HOSH 的净偶极矩为 1.60D，而 HSSH 的净偶极矩为 1.15D。由于它们的强度差异显著，HOSH 可能是这两种分子中更有可能通过振动光谱进行天文观测的候选者，但由于它们的净偶极矩都足够大，因此可以通过旋转光谱检测到它们，以发现它们在密集 ISM 中作为可能的分子硫汇的作用。
