论文标题
天文相关的冰混合物中复杂有机分子的红外光谱。 V.氰化物（乙腈）
Infrared spectra of complex organic molecules in astronomically relevant ice mixtures. V. Methyl cyanide (acetonitrile)
论文作者
论文摘要
地面望远镜的敏感性和分辨率的提高使得能够在各种环境中检测气相复合有机分子（COM）。预计许多检测到的物种将在星际颗粒的冰表面形成，然后转移到气相中。因此，冰冷的材料被视为ISM中COM的原始源。即将到来的恒星形成区域中星际冰的JWST观察将揭示具有前所未有的分辨率和灵敏度的冷冻分子的IR特征。为了识别JWST数据中的COM功能，需要用于模拟星际环境的条件的IC的实验室IR光谱。这项工作呈现FTIR Spectra（500-4000 cm $^{ - 1} $/20-2.5 $ $ $ m，分辨率为1 cm $^{ - 1} $的甲基甲烷（CH $ _3 $ CN，aka acotonitrile），aka acotonitrile） 15-150 K的温度。还测量了纯无非晶的CH $ _3 $ CN冰的折射率，并测量了所选IR频段的带强度，峰位置和FWHM。这些频带是：Ch $ _3 $ SYMSTRESTing在2940.9 cm $^{ - 1} $中，CN伸展为2252.2 cm $^{ - 1} $，模式的组合为1448.3 cm $ $^{ - 1} $，CH $ _3 $ _3 $ _3 $ antism antisym def。在1410 cm $^{ - 1} $，ch $ _3 $ sym def。在1374.5 cm $^{ - 1} $，以及1041.6 cm $^{ - 1} $的Ch $ _3 $ rock。将CH $ _3 $ CN的实验室光谱与对W33A和三个低质量YSO的ICE的观察结果进行了比较。由于无法对CH $ _3 $ CN的明确识别，因此CH $ _3 $ CN列密度的上限确定为$ \ \ leq 2.4 \ times 10^{17} $分子CM $ $^{ - 2} $ W33A和$ 5.2 \ \ \ \ \ \ 5.2 \ \ \ \ \ \ \ \ \ \ \ \ \ \ $ 5.2 {16} $，$ 1.9 TIESE，$ 1.9 TIESTES 1.9 tiese and $ 1.9^tipes and 1.9 tipes and $ 1.9^tipes 1.9 tipes and 1.9 tipes and $ 1.9^3.8} 10^{16} $分子CM $^{ - 2} $分别用于IRAS，IRAS 03235和L1455 IRS3。 W.R.T实心H $ _2 $ O，这些值分别对应于W33A，EC92，IRAS 03235和L1455 IRS3的相对丰度1.9、3.1、1.3和4.1 \％。
The increasing sensitivity and resolution of ground-based telescopes have enabled the detection of gas-phase complex organic molecules (COMs) across a variety of environments. Many of the detected species are expected to form on the icy surface of interstellar grains and transfer later into the gas phase. Therefore, icy material is regarded as a primordial source of COMs in the ISM. Upcoming JWST observations of interstellar ices in star-forming regions will reveal IR features of frozen molecules with unprecedented resolution and sensitivity. To identify COM features in the JWST data, lab IR spectra of ices for conditions that simulate interstellar environments are needed. This work presents FTIR spectra (500-4000 cm$^{-1}$/20-2.5$μ$m, with a resolution of 1 cm$^{-1}$) of methyl cyanide (CH$_3$CN, aka acetonitrile) mixed with H$_2$O, CO, CO$_2$, CH$_4$, and NH$_3$, at temperatures from 15-150 K. The refractive index of pure amorphous CH$_3$CN ice at 15K and the band strength, peak position, and FWHM of selected IR bands are also measured. These bands are: the CH$_3$ sym stretching at 2940.9 cm$^{-1}$, the CN stretching at 2252.2 cm$^{-1}$, a combination of modes at 1448.3 cm$^{-1}$ , the CH$_3$ antisym def. at 1410 cm$^{-1}$ , the CH$_3$ sym def. at 1374.5 cm$^{-1}$, and the CH$_3$ rock at 1041.6 cm$^{-1}$. The lab spectra of CH$_3$CN are compared to observations of ices toward W33A and three low-mass YSOs. Since an unambiguous identification of CH$_3$CN is not possible, upper limits for the CH$_3$CN column density are determined as $\leq 2.4\times 10^{17}$ molecules cm$^{-2}$ for W33A and $5.2 \times 10^{16}$, $1.9\times 10^{17}$, and $3.8\times 10^{16}$ molecules cm$^{-2}$ for EC92, IRAS 03235, and L1455 IRS3, respectively. W.r.t solid H$_2$O, these values correspond to relative abundances of 1.9, 3.1, 1.3, and 4.1\%, for W33A, EC92, IRAS 03235, and L1455 IRS3, respectively.
