Abstract Acrylonitrile (ALN) and acetonitrile (ATN) are two important interstellar molecules that contain nitrogen atoms. Herein, we explore the proton transfer processes occurring in gaseous clusters of ALN and ATN molecules with the aid of synchrotron vacuum ultraviolet radiation. We investigated the proton transfer phenomenon by use of time-of-flight mass spectrometry as well as theoretical calculations. We observe that the mass spectra of ALN and ATN clusters are apparently different from each other. In the mass spectrum of ALN clusters, the peaks related to un-protonated cluster cations are dominant. Unlike the ALN clusters, the protonated cluster cations are dominant in the mass spectrum of ATN clusters. These results are attributed to the different conjugate and hyperconjugate molecular structures in ALN and ATN, respectively. Theoretical calculations show that the conjugation effect between the πC=C orbital and πC≡N orbital in ALN induces a high proton transfer barrier that determines the dominant peaks of its non-protonated clusters cations. Conversely, the hyperconjugation between the σCα-H and πC≡N orbital in the ATN molecule determines that the proton transfer process in ATN is a low-barrier or even a no-barrier process. This favors the formation of protonated clusters. The present results reveal that ALN clusters are more aprotic than those consisting of ATN, and a relative high energy barrier is needed to surmount the proton transfer process of ALN clusters. This property of ALN makes it an appropriate candidate molecule to form the membrane alternative in the liquid methane lakes of Titan. ATN is not an appropriate candidate.

中文翻译：

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同步辐射下星际分子簇中的质子转移过程：以丙烯腈和乙腈二聚体为例

摘要 丙烯腈（ALN）和乙腈（ATN）是两种重要的含有氮原子的星际分子。在此，我们借助同步加速器真空紫外辐射探索在 ALN 和 ATN 分子的气态团簇中发生的质子转移过程。我们通过使用飞行时间质谱和理论计算研究了质子转移现象。我们观察到 ALN 和 ATN 簇的质谱明显不同。在 ALN 簇的质谱中，与未质子化簇阳离子相关的峰占主导地位。与 ALN 簇不同，质子化簇阳离子在 ATN 簇的质谱中占主导地位。这些结果分别归因于 ALN 和 ATN 中不同的共轭和超共轭分子结构。理论计算表明，ALN 中 πC=C 轨道和 πC≡N 轨道之间的共轭效应引起了高质子转移势垒，这决定了其非质子化簇阳离子的主峰。相反，ATN分子中σCα-H和πC≡N轨道之间的超共轭决定了ATN中的质子转移过程是低势垒甚至无势垒过程。这有利于质子化簇的形成。目前的结果表明，ALN 簇比由 ATN 组成的簇更具非质子性，并且需要相对较高的能垒来克服 ALN 簇的质子转移过程。ALN 的这一特性使其成为在泰坦液态甲烷湖中形成膜替代物的合适候选分子。ATN 不是合适的候选人。