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The detection of nitrile-containing species in the interstellar medium has highlighted the role of cyano derivatives as proxies for the corresponding non-polar hydrocarbons. Among them, cinnamonitrile can be regarded as a styrene analogue with enhanced polarity, and, thus, as a promising astrochemical candidate. Here, we report the first characterization of its rotational spectrum, combining quantum-chemical calculations and the so-called “Lego-brick” approach with broadband measurements in the 2-18 GHz range. Both E- and Z-cinnamonitrile have been identified in the spectrum, and accurate rotational, centrifugal distortion, and nitrogen quadrupole coupling constants have been obtained. Moreover, 15N- and 13C-containing isotopologues of the most stable E form have been observed in natural abundance and enabled the determination of a (partial) semi-experimental equilibrium structure. Special care was devoted to the treatment of the lowest-frequency torsional mode, whose anharmonicity required a tailored strategy in order to achieve a structure consistent with theoretical predictions. Our results provide both a reliable spectroscopic foundation for astronomical searches of cinnamonitrile and new insights into the structural flexibility of styrene derivatives which will be further explored in future works.
Melosso et al. (Tue,) studied this question.