Abstract The microwave spectrum of methyl n-propyl sulfide, CH3-S-CH2-CH2-CH3, was recorded in the frequency region from 2.0 to 26.5 GHz, revealing three conformers. Quantum chemical calculations were carried out to support the experimental work. Fine splittings arising from the internal rotation of the methyl group attached to the sulfur atom were resolved and analyzed. Torsional barriers of about 600 cm−1 for the two conformers with C1 symmetry and about 700 cm−1 for the Cs conformer could be deduced, showing that the conformations affect the methyl internal rotation. Torsional splittings of the methyl group at the end of the propyl moiety were observed for some transitions, leading to the determination of barrier heights close to 1000 cm−1. The spectrum of the 34S isotopologue of the most stable conformer could be measured in natural abundance. The present laboratory work provides highly accurate spectroscopic parameters, which serve as reliable starting values for extrapolation in higher frequency ranges and for the search of this sulfur-containing molecule in the interstellar medium.

中文翻译：

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甲基正丙基硫化物的实验室旋转光谱：构象分析和甲基内旋

摘要 甲基正丙基硫醚 CH3-S-CH2-CH2-CH3 的微波光谱记录在 2.0 至 26.5 GHz 的频率范围内，揭示了三个构象异构体。进行了量子化学计算以支持实验工作。解析和分析由连接到硫原子的甲基的内部旋转引起的精细分裂。可以推断出两个具有 C1 对称性的构象异构体的扭转势垒约为 600 cm-1，而 Cs 构象异构体的扭转势垒约为 700 cm-1，表明这些构象影响了甲基内旋。在某些转变中观察到丙基部分末端甲基的扭转分裂，导致势垒高度接近 1000 cm-1。最稳定的构象异构体的 34S 同位素体的光谱可以以天然丰度进行测量。