C5H9N异构体：可能的支链星际分子的指针
C5H9N Isomers: Pointers to Possible Branched Chain Interstellar Molecules
摘要：
异丙基氰化物的天文观测进一步强调了ISM的化学成分和陨石的分子组成之间的联系，其中支链氨基酸比直链氨基酸占主导地位。然而，在ISM中对更多支链分子的观察将坚定地建立这种联系。根据这一点，我们已经考虑了C5H9N异构体组中的下一个更高的成员的烷基氰化物和其他支链异构体属于。高层次的量子化学计算已被用于估计这些异构体的准确能量。从结果来看，正丁基氰化物是天文学上搜索过的唯一异构体，不是最稳定的异构体，因此，这可能解释了为什么它的搜索只能得到其柱密度的上限而没有成功检测。相反，该基团的两种最稳定的异构体是支链异构体，叔丁腈和异丁腈。基于这些异构体的旋转常数，它被发现，叔丁腈的预期强度是最大的异构体中的基团。因此，这被认为是天文观测的最有可能的候选者。一个简单的LTE（局部热力学平衡）建模也进行了检查的可能性检测叔丁基氰化物在毫米波区域。
英文摘要：
The astronomical observation of isopropyl cyanide further stresses the link between the chemical composition of the ISM and molecular composition of the meteorites in which there is a dominance of branched chain amino acids as compared to the straight. However, observations of more branched chain molecules in ISM will firmly establish this link. In the light of this, we have considered C5H9N isomeric group in which the next higher member of the alkyl cyanide and other branched chain isomers belong. High-level quantum chemical calculations have been employed in estimating accurate energies of these isomers. From the results, the only isomer of the group that has been astronomically searched, n-butyl cyanide is not the most stable isomer and therefore, which might explain why its search could only yield upper limits of its column density without a successful detection. Rather, the two most stable isomers of the group are the branched chain isomers, tert-butylnitrile and isobutyl cyanide. Based on the rotational constants of these isomers, it is found that the expected intensity of tert-butylnitrile is the maximum among this isomeric group. Thus, this is proposed as the most probable candidate for astronomical observation. A simple LTE (Local thermodynamic equilibrium) modelling has also been carried out to check the possibility of detecting tert-butyl cyanide in the millimetre-wave region.
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