Rotational spectra of methyl cyanide were recorded newly and were analyzed together with existing spectra to extend the global model of low-lying vibrational states and their interactions to ${\upsilon }_4=1$ 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 CH₃CN is obtained from IR spectra. A spectrum of $2{\nu }_8$ around 717 cm⁻¹, analyzed in our previous study, covered also the ${\nu }_4$ 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 ${\upsilon }_4=1$ appears to be with ${\upsilon }_8=3$, $\mathrm{\Delta }K=0,\mathrm{\Delta }l=+3$, a previously characterized anharmonic resonance. We report new analyses of interactions with $\mathrm{\Delta }K=-2$ and $\mathrm{\Delta }l=+1$, with $\mathrm{\Delta }K=-4$ and $\mathrm{\Delta }l=-1$, and with $\mathrm{\Delta }K=-6$ and $\mathrm{\Delta }l=-3$; these four types of interactions connect all l substates of ${\upsilon }_8=3$ in energy to ${\upsilon }_4=1$. A known $\mathrm{\Delta }K=-2,\mathrm{\Delta }l=+1$ interaction with ${\upsilon }_7=1$ was also analyzed, and investigations of the $\mathrm{\Delta }K=+1$, $\mathrm{\Delta }l=-2$ and $\mathrm{\Delta }K=+3,\mathrm{\Delta }l=0$ resonances with ${\upsilon }_8=2$ were improved, as were interactions between successive states with ${\upsilon }_8⩽3$, mainly through new ${\upsilon }_8⩽2$ rotational data.

A preliminary single state analysis of the ${\upsilon }_4={\upsilon }_8=1$ state was carried out based on rotational transition frequencies and on ${\nu }_4+{\nu }_8-{\nu }_8$ 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 ${\upsilon }_4={\upsilon }_8=1$.

In addition to the interstellar detection of rotational transitions of methyl cyanide from within all vibrational states up to ${\upsilon }_4=1$, we report the tentative detection of ${\upsilon }_4={\upsilon }_8=1$ toward the main hot molecular core of the protocluster Sagittarius B2(N) employing the Atacama Large Millimeter/submillimeter Array.

记录了甲基氰化物的旋转光谱，并与现有光谱一起进行了分析，以扩展低层振动状态及其相互作用的全局模型。 ${\upsilon }_4=\mathrm{1个}$在920 cm ^-1处。旋转光谱覆盖了36–1439 GHz区域的大部分，并且分别达到了79和16的量子数J和K。从IR光谱获得关于CH ₃ CN的K能级结构的信息。一系列$\mathrm{2个}{\nu }_8$在我们先前的研究中分析，大约717 cm ^-1的范围还包括${\nu }_4$乐队。该频带的分配范围为880–952 cm ^-1，分别获得的量子数J和K为61和13。

最重要的互动 ${\upsilon }_4=\mathrm{1个}$ 似乎与 ${\upsilon }_8=3$， $\mathrm{\Delta }ķ=0，\mathrm{\Delta }升=+3$，以前表征为非谐共振。我们报告了与$\mathrm{\Delta }ķ=--\mathrm{2个}$ 和 $\mathrm{\Delta }升=+\mathrm{1个}$， 和 $\mathrm{\Delta }ķ=--4$ 和 $\mathrm{\Delta }升=--\mathrm{1个}$， 与 $\mathrm{\Delta }ķ=--6$ 和 $\mathrm{\Delta }升=--3$; 这四种类型的相互作用将的所有l个子状态连接在一起${\upsilon }_8=3$ 在精力上 ${\upsilon }_4=\mathrm{1个}$。一个已知的$\mathrm{\Delta }ķ=--\mathrm{2个}，\mathrm{\Delta }升=+\mathrm{1个}$ 与...互动 ${\upsilon }_7=\mathrm{1个}$ 还进行了分析，并对 $\mathrm{\Delta }ķ=+\mathrm{1个}$， $\mathrm{\Delta }升=--\mathrm{2个}$ 和 $\mathrm{\Delta }ķ=+3，\mathrm{\Delta }升=0$ 与共鸣 ${\upsilon }_8=\mathrm{2个}$ 以及连续状态之间的相互作用得到了改善 ${\upsilon }_8⩽3$，主要是通过新 ${\upsilon }_8⩽\mathrm{2个}$ 旋转数据。

初步的单态分析 ${\upsilon }_4={\upsilon }_8=\mathrm{1个}$ 状态是根据旋转跃迁频率和 ${\nu }_4+{\nu }_8--{\nu }_8$热点数据。尽管有明显的广泛扰动，但相当一部分的K水平全部或部分在不确定性内得以复制。${\upsilon }_4={\upsilon }_8=\mathrm{1个}$。

除了星际探测，从所有振动状态一直到 ${\upsilon }_4=\mathrm{1个}$，我们报告了对的初步检测 ${\upsilon }_4={\upsilon }_8=\mathrm{1个}$ 使用Atacama大毫米/亚毫米阵列向射手座人马座B2（N）的主要热分子核方向移动。