Cyanoacetylene, HCC–CN is a ubiquitous molecule in the Universe. However, its interstellar chemistry is not well understood and its understanding requires laboratory data including rotational spectroscopy of possible products coming from a reaction with another compounds. In this study we present the first spectroscopic characterization of gauche conformation of 4-hydroxy-2-butynenitrile (HOCH₂CCCN), a formal adduct of cyanoacetylene on formaldehyde, in the frequency range up to 500 GHz. The analysis of the rotational spectrum was complicated by internal rotation of the OH group that connects two equivalent gauche configurations. The spectral assignment was aided by high-level quantum chemical calculations that were particularly useful in the interpretation of torsional–rotational part of the problem. The applied reduced-axis-system (RAS) formalism allowed fitting within experimental accuracy the lines with K_a < 18. We also present the method of search for initial global solution of torsional–rotational problem within RAS formalism. Accurate spectroscopic parameters obtained in this study provide a reliable basis for the detection of 4-hydroxy-2-butynenitrile in the interstellar medium.

中文翻译：

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毫米波光谱法研究4-羟基-2-丁腈中OH基的内旋

氰基乙炔，HCC-CN是宇宙中普遍存在的分子。然而，对其星际化学的了解还不够，需要了解实验室数据，包括对与另一种化合物反应产生的可能产物进行旋转光谱的实验室数据。在这项研究中，我们提出了在高达500 GHz的频率范围内，4-羟基-2-丁腈（HOCH ₂ CCCN）（氰基乙炔在甲醛上的正式加成物）的gauche构象的首次光谱表征。连接两个等效gauche的OH基团的内部旋转使旋转光谱的分析变得复杂配置。光谱分配得到了高级量子化学计算的帮助，这在解释问题的扭转-旋转部分时特别有用。所应用的减小轴系统（RAS）形式主义允许在实验精度内拟合K _a <18的线。我们还提出了在RAS形式主义中寻找扭转-旋转问题的整体解的方法。在这项研究中获得的准确的光谱参数为星际介质中的4-羟基-2-丁腈的检测提供了可靠的基础。