Abstract The molecular structure of 3-methylpyrrole in the gas phase has been determined using a combination of high-resolution spectroscopy and quantum chemical calculations. The rotational spectrum was recorded using a molecular jet Fourier transform microwave spectrometer covering the frequency range from 2.0 to 26.5 GHz. The experimental data were analyzed using the programs XIAM and BELGI-Cs-hyperfine. Because the internal rotor axis accidentally lies along the principal a-axis of inertia, the rho axis system and the principal axis system coincide, enabling a direct comparison of the fits. With the program XIAM, the rotational constants A = 8631.1629(12), B = 3342.19750(43), and C = 2445.73846(42) MHz were obtained. Torsional splittings due to internal rotation of the methyl group were observed, leading to the determination of the V3 potential of 245.92445(31) cm−1. Hyperfine splittings arising from the nuclear quadrupole coupling of the 14N nucleus could be resolved, and the quadrupole coupling constants χaa = 1.4159(49) and χbb − χcc = 4.1622(86) MHz were found.

中文翻译：

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通过微波光谱研究 3 甲基吡咯中的 14N 核四极杆耦合和甲基内旋

摘要 气相中 3-甲基吡咯的分子结构已使用高分辨率光谱和量子化学计算的组合确定。使用分子喷射傅里叶变换微波光谱仪记录旋转光谱，覆盖频率范围为 2.0 至 26.5 GHz。使用程序 XIAM 和 BELGI-Cs-hyperfine 分析实验数据。由于内部转子轴意外地位于惯性主轴 a 轴上，因此 rho 轴系统和主轴系统重合，从而可以直接比较拟合。使用 XIAM 程序，获得了旋转常数 A = 8631.1629(12)、B = 3342.19750(43) 和 C = 2445.73846(42) MHz。观察到由于甲基的内部旋转引起的扭转分裂，导致确定 245.92445(31) cm-1 的 V3 电位。可以解决由 14N 核的核四极耦合引起的超精细分裂，并且发现了四极耦合常数 χaa = 1.4159(49) 和 χbb − χcc = 4.1622(86) MHz。