Cabezas C, Neeman E M, Tercero B, Bermúdez C, Cernicharo J
Instituto de Física Fundamental (IFF-CSIC). Group of Molecular Astrophysics, C/Serrano 123, 28006 Madrid, Spain.
Departamento de Química Física. Facultad de Ciencias y Tecnologías Químicas. Universidad de Castilla-La Mancha. Avda. Camilo José Cela 1B. 13071, Ciudad Real, Spain.
Astron Astrophys. 2021 Jan 15;645. doi: 10.1051/0004-6361/202039924. eCollection 2021 Jan.
At least a dozen molecules with a formyl group (HCO) have been observed to date in the interstellar medium (ISM), suggesting that other such species exist and remain to be discovered. However, there is still a lack of high-resolution spectroscopic data for simple molecular species of this type that could provide a basis for their detection.
Cyclopropanecarboxaldehyde, c-CHCHO, is a small molecule containing a formyl group and is therefore an interesting candidate for astrophysical detection. The rotational spectrum of cyclopropanecarboxaldehyde has been observed before, but its experimental rotational parameters are not precise enough to allow its detection in the millimetre-wave domain.
We measured the rotational spectrum of cyclopropanecarboxaldehyde in the frequency ranges 31.5-50 GHz and 72-116.5 GHz using the GACELA (GAS CEll for Laboratory Astrophysics) broadband high-resolution rotational spectrometer constructed at the Yebes Observatory. The spectroscopic study was supported by high-level theoretical calculations which were used in the identification of the vibrational excited states of cyclopropanecarboxaldehyde.
Our analysis of the rotational spectrum of cyclopropanecarboxaldehyde allowed us to obtain accurate rotational parameters for the ground state of both cis and trans isomers, which were used to derive sufficiently reliable predictions up to 300 GHz. In addition to the ground states, we identified 12 and 6 vibrationally excited states for the trans and cis isomers, respectively, including fundamental modes, multiple excitation quanta, and combination states. We find that the gas phase concentration of the trans isomer is almost 1.2 times larger than that of the cis one. These new experimental rotational parameters were employed to search for cyclopropanecarboxaldehyde in the warm molecular clouds Orion KL and Sgr B2(N) using the spectral surveys captured by ALMA (Orion) and IRAM 30 m (Sgr) at 1 mm and 3 mm, respectively.
迄今为止，在星际介质（ISM）中已观测到至少十二种带有甲酰基（HCO）的分子，这表明其他此类物种存在且有待发现。然而，对于这类简单分子物种，仍然缺乏高分辨率光谱数据，而这些数据可为其探测提供依据。
环丙烷甲醛（c-CH₂CHO）是一种含有甲酰基的小分子，因此是天体物理探测的一个有趣候选物。环丙烷甲醛的转动光谱此前已被观测到，但其实验转动参数不够精确，无法在毫米波波段进行探测。
我们使用在耶贝斯天文台建造的GACELA（用于实验室天体物理学的气体池）宽带高分辨率转动光谱仪，在31.5 - 50 GHz和72 - 116.5 GHz频率范围内测量了环丙烷甲醛的转动光谱。光谱研究得到了高水平理论计算的支持，这些计算用于识别环丙烷甲醛的振动激发态。
我们对环丙烷甲醛转动光谱的分析使我们能够获得顺式和反式异构体基态的精确转动参数，这些参数被用于得出高达300 GHz的足够可靠的预测。除了基态，我们分别为反式和顺式异构体识别出了12个和6个振动激发态，包括基模、多激发量子态和组合态。我们发现反式异构体的气相浓度几乎是顺式异构体的1.2倍。这些新的实验转动参数被用于分别使用阿塔卡马大型毫米波/亚毫米波阵列（ALMA，用于猎户座KL）和IRAM 30米望远镜（用于人马座B2（N））在1毫米和3毫米波段捕获的光谱调查，在温暖分子云猎户座KL和人马座B2（N）中搜索环丙烷甲醛。
