The microwave spectrum of the dimer Ar–1,3-difluorobenzene from 2 to 18 GHz is reported. The spectrum has been observed using a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer that has recently been expanded to include the 2–6 GHz region of the electromagnetic spectrum. Details of this upgraded spectrometer are reported. Eighty-seven transitions were observed for the parent dimer spectrum, which was adequately fit to a semirigid rotational Hamiltonian consisting of A, B, and C as well as four quartic centrifugal distortion constants. Observations of ¹³C species in natural abundance were aided by utilizing smaller chirp ranges of 7–9 and 9–11 GHz for 1.9 million and 3.73 million averages, respectively. Assignment of ¹³C isotopologues allowed for determination of the Kraitchman coordinates of the carbon atoms as well as inertial fits of the complex. The quantum-chemical structure predicts an Ar to monomer center of mass distance of 3.48 Å, compared with 3.564(1) Å determined from experimental structural analysis. This new study indicates that in fluorinated benzene–Ar dimers, when the fluorines are separated by more carbon atoms, the Ar–ring center distance decreases.

中文翻译：

---

Ar–1,3-二氟苯的微波光谱和结构

据报道，二聚体Ar–1,3-二氟苯的微波光谱范围为2至18 GHz。使用a脉冲傅立叶变换微波（CP-FTMW）光谱仪可以观察到该光谱，该光谱仪最近已扩展到包括2-6 GHz的电磁光谱范围。报告了此升级版光谱仪的详细信息。观察到二聚体光谱的八十七个跃迁，该跃迁足够适合由A，B和C组成的半刚性旋转哈密顿量以及四个四次离心畸变常数。通过利用较小的7–9 GHz和9–11 GHz线性调频范围分别平均190万和373万，对¹³种C物种的自然丰度进行了辅助。分配¹³ C同位素异构体可用于确定碳原子的Kraitchman坐标以及配合物的惯性拟合。量子化学结构预测的Ar到单体质量中心的距离为3.48Å，而根据实验结构分析得出的值为3.564（1）Å。这项新的研究表明，在氟化苯-Ar二聚体中，当氟被更多的碳原子分隔时，Ar-环的中心距离减小。