对太空复杂分子的探索：毫米波区域正丁腈（n-C4H9CN）的实验室光谱及其在人马座的天文搜索B2（N）
The quest for complex molecules in space: Laboratory spectroscopy of n-butyl cyanide, n-C4H9CN, in the millimeter wave region and its astronomical search in Sagittarius B2(N)
摘要：
最近在人马座B2（N）中检测到饱和正丙基氰化物。下一个较大的无支链烷基氰化物是正丁基氰化物。我们提供了精确的静止频率预测超出毫米波范围，在银河系中心源人马座B2（N）中寻找这种分子，并促进其在太空中的探测。我们研究了$n$ -丁基氰在75 GHz和348 GHz之间的实验室转动光谱。我们在人马座B2（N）的灵敏IRAM 30 m分子线调查中寻找分子产生的发射线。我们确定了一千多个旋转转换在实验室中的三个构象的有限的数据已获得以前在分子束微波研究。量子数范围大大扩展到J ~ 120或更大，Ka > 35，导致精确的光谱参数和精确的静止频率计算高达约500 GHz的两个较低能量构象的强到中等弱的跃迁。对于两种较低能量的构象，anti-anti和gauche-anti，柱密度的上限分别为N <= 3 x 10 E15 cm-2和8 x 10 E15 cm-2，它们分别朝向人马座B2（N）。我们目前的数据将有助于识别正丁基氰化物在毫米或更长的波长与射电望远镜阵列，如ALMA，NOEMA，或EVLA。特别是，它的检测人马座B2（N）与ALMA似乎可行。
英文摘要：
The saturated n-propyl cyanide was recently detected in Sagittarius B2(N). The next larger unbranched alkyl cyanide is n-butyl cyanide. We provide accurate rest frequency predictions beyond the millimeter wave range to search for this molecule in the Galactic center source Sagittarius B2(N) and facilitate its detection in space. We investigated the laboratory rotational spectrum of $n$-butyl cyanide between 75 GHz and 348 GHz. We searched for emission lines produced by the molecule in our sensitive IRAM 30 m molecular line survey of Sagittarius B2(N). We identified more than one thousand rotational transitions in the laboratory for each of the three conformers for which limited data had been obtained previously in a molecular beam microwave study. The quantum number range was greatly extended to J ~ 120 or more and Ka > 35, resulting in accurate spectroscopic parameters and accurate rest frequency calculations up to about 500 GHz for strong to moderately weak transitions of the two lower energy conformers. Upper limits to the column densities of N <= 3 x 10E15 cm-2 and 8 x 10E15 cm-2 were derived towards Sagittarius B2(N) for the two lower energy conformers, anti-anti and gauche-anti, respectively. Our present data will be helpful for identifying n-butyl cyanide at millimeter or longer wavelengths with radio telescope arrays such as ALMA, NOEMA, or EVLA. In particular, its detection in Sagittarius B2(N) with ALMA seems feasible.
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