2-Chloro-4-fluorotoluene was investigated using a combination of molecular jet Fourier transform microwave spectroscopy in the frequency range from 5 to 21 GHz and quantum chemistry. The molecule experiences an internal rotation of the methyl group, which causes fine splittings of all rotational transitions into doublets with separation on the order of a few tens of kHz. In addition, hyperfine effects originating from the chlorine nuclear quadrupole moment coupling its nuclear spin to the end-over-end rotation of the molecule are observed. The torsional barrier was derived using both the rho and the combined-axis-method, giving a value of 462.5(41) cm⁻¹. Accurate rotational constants and quadrupole coupling constants were determined for the ³⁵Cl and ³⁷Cl isotopologues and compared with Bailey’s semi-experimental quantum chemical predictions. The gas phase molecular structure was deduced from the experimental rotational constants supplemented with those calculated by quantum chemistry at various levels of theory. The values of the methyl torsional barrier and chlorine nuclear quadrupole coupling constants were compared with the theoretical predictions and with those of other chlorotoluene derivatives.

结合使用了5-21 GHz范围内的分子喷射傅里叶变换微波光谱和量子化学技术，研究了2-氯-4-氟甲苯。分子经历甲基的内部旋转，这导致所有旋转跃迁的精细分裂成二重峰，其间隔约为几十kHz。另外，观察到源自其核自旋耦合至分子的末端-末端旋转的氯核四极矩的超精细效应。使用rho和组合轴方法都可以得出扭转势垒，其值为462.5（41）cm ^-1。确定了³⁵ Cl和^37的精确旋转常数和四极耦合常数Cl同位素分子，并与Bailey的半实验量子化学预测相比较。从实验旋转常数推导出气相分子结构，并在各种理论水平上用量子化学计算得出。将甲基扭转屏障和氯核四极偶合常数的值与理论预测值以及其他氯代甲苯衍生物的值进行了比较。