揭示气相H2NCO自由基：实验室转动光谱及对IRAS 16293-2422的星际搜寻
Unveiling gas phase H2NCO radical: Laboratory rotational spectroscopy and interstellar search toward IRAS 16293-2422
AI总结：
本研究通过毫米和亚毫米波纯转动光谱首次在气相中探测到H2NCO自由基，导出了其基振态的精确光谱参数，并在IRAS 16293-2422的PILS巡天中未检测到该自由基，推断其丰度上限与物理化学模型预测相符。
摘要：
背景。氨基甲酰自由基（H2NCO）被认为在甲酰胺和乙酰胺等关键星际复杂有机分子的冰面化学中发挥着核心作用。然而，人们对这种在实验室气相实验中仍难以捉摸的自由基知之甚少。目标。为了实现H2NCO的星际搜寻，我们对其纯转动光谱进行了必要的实验室表征。方法。我们报道了H2NCO的气相实验室探测，它通过甲酰胺的H原子抽提产生，利用了毫米和亚毫米波长的纯转动光谱。毫米波数据使用啁啾脉冲傅里叶变换光谱获取，而亚毫米波数据则使用塞曼调制光谱获得。实验测量由$ω$B97X-D/cc-pVQZ理论水平的量子化学计算指导。对该自由基的星际搜寻已在原恒星干涉谱线巡天（PILS）中针对太阳型原恒星IRAS 16293-2422展开。结果。通过对高达660 GHz的实验跃迁进行指认和拟合，导出了H2NCO在其基振态下的可靠光谱参数，从而实现了精确的光谱预测。在PILS巡天中未检测到该自由基的跃迁。推断出的上限表明，在该源中H2NCO的丰度比甲酰胺低至少60倍，比HNCO低至少160倍；这一数值与该年轻原恒星的物理化学模型预测相符。
英文摘要：
Context. The carbamoyl radical (H2NCO) is believed to play a central role in the ice-grain chemistry of crucial interstellar complex organic molecules as formamide and acetamide. Yet, little is known about this radical that remains elusive in laboratory gas-phase experiments. Aims. In order to enable interstellar searches of H2NCO, we have undertaken a mandatory laboratory characterisation of its pure rotational spectrum. Methods. We report the gas-phase laboratory detection of H2NCO, produced by H-atom abstraction from formamide, using pure rotational spectroscopy at millimetre and submillimetre wavelengths. Millimetre-wave data were acquired using chirped-pulse Fourier-transform spectroscopy while submillimetre-wave ones were obtained using Zeeman-modulated spectroscopy. Experimental measurements were guided by quantum-chemical calculations at the $ω$B97X-D/cc-pVQZ level of theory. Interstellar searches for the radical have been undertaken on the Protostellar Interferometric Line Survey (PILS) towards the solar-type protostar IRAS 16293-2422. Results. From the assignment and fit of experimental transitions up to 660 GHz, reliable spectroscopic parameters for H2NCO in its ground vibrational state have been derived, enabling accurate spectral predictions. No transitions of the radical were detected on the PILS survey. The inferred upper limit shows that H2NCO abundance is at least 60 times below that of formamide and 160 times below that of HNCO in this source; a value that is in agreement with predictions from a physico-chemical model of this young protostar.
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