The azirinyl cation is an aromatic cyclic molecule that is isoelectronic with cyclopropenylidene, c-C3H2, and c-C3H3+. Cyclopropenylidene has been shown to be ubiquitous, existing in many different astrophysical environments. Given the similar chemistry between C and N, and the relative abundances between C and N in astrophysical environments, it is expected that there should be aromatic ringed molecules that incorporate N in the ring, but as yet, no such molecule has been identified. To address this issue, the present study uses high levels of electronic structure theory to compute a highly accurate quartic force field (QFF) for the azirinyl cation and its two lowest lying isomers, the cyanomethyl and isocyanomethyl cations. The theoretical approach uses the singles and doubles coupled-cluster method that includes a perturbative correction for connected triple excitations, CCSD(T), together with extrapolation to the one-particle basis set limit and corrections for scalar relativity and core-correlation. The QFF is then used in a second-order vibrational perturbation theory analysis (VPT2) to compute the fundamental vibrational frequencies and rovibrational spectroscopic constants for all three C2NH2+ isomers. The reliability of the VPT2 vibrational frequencies is tested by comparison to vibrational configuration interaction (VCI) calculations, and excellent agreement is found between the two approaches. Fundamental vibrational frequencies and rovibrational spectroscopic constants for all singly substituted 13C, 15N, and D isotopologues are also reported. It is expected that the highly accurate spectroscopic data reported herein will be useful in the identification of these cations in high-resolution experimental or astronomical observations.

中文翻译：

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叠氮基阳离子（c-C2NH2 +）及其异构体的高精度四次力场和振动光谱常数。

叠氮基阳离子是与环丙烯基，c-C3H2和c-C3H3 +等电子的芳族环状分子。环丙烯基被证明是普遍存在的，存在于许多不同的天体环境中。鉴于C和N之间的化学性质相似，以及在天体环境中C和N之间的相对丰度，可以预期应该有在环中掺入N的芳香环分子，但到目前为止，尚未发现这种分子。为了解决这个问题，本研究使用高水平的电子结构理论为叠氮基阳离子及其两个最低的异构体氰基甲基和异氰基甲基阳离子计算出了高精度的四方力场（QFF）。该理论方法使用单双联耦合群集方法，该方法包括对连接的三重激发CCSD（T）的微扰校正，以及对单粒子基集极限的外推以及对标量相对性和核相关性的校正。然后将QFF用于二阶振动摄动理论分析（VPT2）中，以计算所有三个C2NH2 +异构体的基本振动频率和振动光谱常数。通过与振动配置相互作用（VCI）计算进行比较，测试了VPT2振动频率的可靠性，并且在两种方法之间发现了极好的一致性。还报告了所有单取代的13C，15N和D同位素异构体的基本振动频率和振动光谱常数。