In this paper, the results of a comprehensive theoretical investigation of neutral HC_nH⁰ and charged HC_nH^± chains are reported using state-of-the-art compound model chemistries (W1BD, G4, CBS-QB3, CBS-APNO, CBS-4M) and single point methods (including “gold standard” CCSD(T)). The properties envisaged include electronic and chemical bonding structure data, enthalpies of formation, adiabatic and vertical ionization (IP), and electron attachment (EA) energies, gas phase acidities, C−H bond strengths, and chain “deprotecting” (HC_nH → H + C_n + H) energies. The best theoretical estimates based on composite models reported here for the various properties investigated agree with the available experimental data and are better than all previous theoretical estimates. To exemplify, for the enthalpies of formation, the G4 composite model achieves a RSMD (root square mean deviation) of 0.28 kcal mol⁻¹ and a MUD (maximum unsigned deviation) of 0.45 kcal mol⁻¹. Most importantly from the astrochemical perspective, it is predicted that the stable HC_nH⁻ anions with $n\le 8$ are nonlinear. Having sufficiently large dipole moments, the anion HC_nH⁻ cis conformers are potential candidates for detection in space via rovibrational spectroscopy.

中文翻译：

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天体化学相关 HCnH 链家族的全面量子化学表征：帮助天文观测的尝试

在本文中，使用最先进的化合物模型化学（W1BD、G4、CBS _- QB3 _、 ^{CBS -} APNO 、CBS-4M）和单点方法（包括“金标准”CCSD(T)）。设想的特性包括电子和化学键结构数据、形成焓、绝热和垂直电离 (IP) 和电子附着 (EA) 能量、气相酸度、C-H 键强度和链“去保护”(HC _n H → H + C _n+ H) 能量。此处报告的基于复合模型的最佳理论估计与所研究的各种特性一致，并且优于所有先前的理论估计。^{例如，对于生成焓，G4 复合模型实现了 0.28 kcal mol -1}的 RSMD（均方根偏差）和 0.45 kcal mol ^-1的 MUD（最大无符号偏差）。最重要的是，从天体化学的角度来看，预计稳定的 HC _n H ^-阴离子具有$n\le 8$是非线性的。具有足够大的偶极矩，阴离子 HC _n H ^- 顺式构象异构体是通过振动光谱在空间中检测的潜在候选者。