Formaldehyde (H₂CO⁺) and methanol (H₃COH⁺) radical cations, well-known in mass spectrometry, potentially form from radiative ionization or ion–molecule reactions in the interstellar medium. For both ions, other tautomeric forms exist that are accessible via [1,2]hydrogen shifts involving reaction barriers in excess of 25 kcal mol^–1. Here, we compute the tunneling rates of the isomerization processes connecting the hydroxymethylene radical cation (HCOH⁺) to its more stable formaldehyde isomer (H₂CO⁺) and the methanol radical cation (H₃COH⁺) to its methylene oxonium isomer (H₂COH₂⁺) using the Wentzel–Kramers–Brillouin method at the CCSD(T)/cc-pVQZ//B3LYP/cc-pVTZ level of theory. While the hydroxymethylene radical cation features a half-life of over 3500 years and thus represents a potentially observable molecule, the methanol radical cation is predicted to decay with a half-life of about 4 days and is thus not likely to be present in appreciable quantities in space. We discuss the potential relevance of the hydroxymethylene and methylene oxonium cations for interstellar carbohydrate formation because both species represent potentially reactive, cationic, carbon-centered radicals.

中文翻译：

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甲醛和甲醇自由基阳离子的势能表面上的隧道异构化

质谱中众所周知的甲醛（H ₂ CO ⁺）和甲醇（H ₃ COH ⁺）自由基阳离子，可能是由星际介质中的辐射电离或离子分子反应形成的。对于这两种离子，都存在其他互变异构形式，可通过涉及反应势垒的[1,2]氢转移超过25 kcal mol ^{–1来获得}。在这里，我们计算了将羟甲基自由基阳离子（HCOH ⁺）连接到其更稳定的甲醛异构体（H ₂ CO ⁺）和将甲醇自由基阳离子（H ₃ COH ⁺）连接到其亚甲基氧鎓异构体（H）的异构化过程的隧穿速率₂ COH ₂ ⁺），使用Wentzel–Kramers–Brillouin方法在CCSD（T）/ cc-pVQZ // B3LYP / cc-pVTZ理论水平上进行。虽然羟亚甲基自由基阳离子具有超过3500年的半衰期，因此代表了一个潜在的可观察分子，但是据预测，甲醇自由基阳离子会以约4天的半衰期衰变，因此不可能以可观的量存在在太空。我们讨论了羟甲基和亚甲基氧鎓阳离子与星际碳水化合物形成的潜在相关性，因为这两种物质都代表潜在的反应性，阳离子，以碳为中心的自由基。