Toward a global model of the interactions in low-lying states of methyl cyanide: rotational and rovibrational spectroscopy of the $v_4 = 1$ state and tentative interstellar detection of the $v_4 = v_8 = 1$ state in Sgr B2(N)
Holger S. P. Müller, Arnaud Belloche, Frank Lewen, Brian J. Drouin, Keeyoon Sung, Robin T. Garrod, Karl M. Menten
通过对新的和已有的乙腈分子转动光谱的分析，将低振动态及其相互作用的整体模型推广到$v_4=1$（920 cm $^{-1}$）.旋转光谱覆盖了36 $-$ 1439 GHz区域的大部分，并分别达到量子数$J$和$K$为79和16。CH $_3$ CN的$K$能级结构的信息由IR光谱获得。在我们以前的研究中分析的717 cm $^{-1}$周围的$2ν_8$光谱也覆盖了$ν_4$带。在这个波段的分配覆盖880 $-$ 952 cm $^{-1}$，获得的量子数$J$和$K$分别为61和13。$v_4=1$最重要的相互作用似乎是与$v_8=3$、$ΔK=0$、$Δl=+3$的相互作用，这是一种先前表征的非谐共振。我们报告了与$ΔK=-2$和$Δl=+1$，与$ΔK=-4$和$Δl=-1$，与$ΔK=-6$和$Δl=-3$相互作用的新分析;这四种类型的相互作用将$v_8=3$的所有$l$亚态能量连接到$v_4=1$。还分析了已知的$ΔK=-2$、$Δl=+1$与$v_7=1$的相互作用，并且改进了对$ΔK=+1$、$Δl=-2$和$ΔK=+3$、$Δl=0$与$v_8=2$的共振的研究，以及主要通过新的$v_8\le 2$旋转数据改进了连续状态与$v_8\le 3$之间的相互作用。基于转动跃迁频率和$ν_4+ν_8-ν_8$热带数据对$v_4=v_8=1$态进行了初步的单态分析。尽管$v_4=v_8=1$存在明显的广泛扰动，但相当一部分$K$水平在不确定性范围内全部或部分重现。利用阿塔卡玛大型毫米波阵列探测到了乙腈从所有振动态到$v_4=1$和$v_4=v_8=1$的转动跃迁，并初步地向人马座B2（N）的热分子核移动。
英文摘要：
New and existing rotational spectra of methyl cyanide were analyzed to extend the global model of low-lying vibrational states and their interactions to $v_4=1$ at 920 cm$^{-1}$. The rotational spectra cover large portions of the 36$-$1439 GHz region and reach quantum numbers $J$ and $K$ of 79 and 16, respectively. Information on the $K$ level structure of CH$_3$CN is obtained from IR spectra. A spectrum of $2ν_8$ around 717 cm$^{-1}$, analyzed in our previous study, covered also the $ν_4$ band. The assignments in this band cover 880$-$952 cm$^{-1}$, attaining quantum numbers $J$ and $K$ of 61 and 13, respectively.
The most important interaction of $v_4=1$ appears to be with $v_8=3$, $ΔK=0$, $Δl=+3$, a previously characterized anharmonic resonance. We report new analyses of interactions with $ΔK=-2$ and $Δl=+1$, with $ΔK=-4$ and $Δl=-1$, and with $ΔK=-6$ and $Δl=-3$; these four types of interactions connect all $l$ substates of $v_8=3$ in energy to $v_4=1$. A known $ΔK=-2$, $Δl=+1$ interaction with $v_7=1$ was also analyzed, and investigations of the $ΔK=+1$, $Δl=-2$ and $ΔK=+3$, $Δl=0$ resonances with $v_8=2$ were improved, as were interactions between successive states with $v_8\le 3$, mainly through new $v_8\le 2$ rotational data.
A preliminary single state analysis of the $v_4=v_8=1$ state was carried out based on rotational transition frequencies and on $ν_4+ν_8-ν_8$ hot band data. A considerable fraction of the $K$ levels was reproduced within uncertainties in its entirety or in part, despite obvious widespread perturbations in $v_4=v_8=1$.
We detect rotational transitions of methyl cyanide from within all vibrational states up to $v_4=1$ and $v_4=v_8=1$ tentatively toward the hot molecular core of Sagittarius B2(N) employing the Atacama Large Millimeter Array.
Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) -- IV. Methyl cyanide isotopologues toward BHR71-IRS1
European Southern Observatory（欧洲南方天文台）；Institut de Recherche en Astrophysique et Planétologie（天体物理与行星学研究所）；Université de Toulouse（图卢兹大学）；CNRS（法国国家科学研究中心）；CNES（法国国家空间研究中心）；Niels Bohr Institute（尼尔斯·玻尔研究所）；University of Copenhagen（哥本哈根大学）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文学研究所）；National Radio Astronomy Observatory（美国国家射电天文台）；Univ. Grenoble Alpes（格勒诺布尔阿尔卑斯大学）；IPAG（格勒诺布尔天体物理与行星学研究所）；National Tsinghua University（国立清华大学）；Physikalisch-Meteorologisches Observatorium Davos und Weltstrahlungszentrum (PMOD/WRC)（达沃斯物理气象观测站暨世界辐射中心）；Universität Bern（伯尔尼大学）；Seoul National University（首尔国立大学）
Rotational spectroscopy as a tool to investigate interactions between vibrational polyads in symmetric top molecules: low-lying states $v_8 \le 2$ of methyl cyanide, CH$_3$CN
Rotational Spectroscopy as a Tool to Study Vibration-Rotation Interaction: Investigations of $^{13}$CH$_3$CN and CH$_3$$^{13}$CN up to $v_8 = 2$ and a Search for $v_8 = 2$ Transitions toward Sagittarius B2(N)
Universität zu Köln（科隆大学）；Max-Planck-Institut für Radioastronomie（马克斯·普朗克射电天文研究所）
