Microwave Spectrum, Dipole Moment and Centrifugal Distortion Constants of 1,2,4-Trifluorobenzene

抄録

The microwave spectrum of 1,2,4-trifluorobenzene has been studied at dry ice temperature in the frequency region of 8 to 12.4 GHz. The molecule exhibits a very dense spectra of both a- and b-type. The analysis of 59 selected transitions from a large number of measured lines yields the following spectroscopic constants of the molecule for Watson’s reduced Hamiltonian in the I^r representation: A=3084.0215±0.0062 MHz, B=1278.3595±0.0027 MHz, C=903.6835±0.0027 MHz, Δ_J=−0.0674±0.0054 kHz, Δ_JK=0.728±0.052 kHz, Δ_K=−0.657±0.016 kHz, δ_J=0.0528±0.0032 kHz and δ_K=−0.574=0.059 kHz. The dipole moment of the molecule has been determined as 1.39±0.03 D. The INDO and CNDO molecular orbital calculations give the value of the dipole moment as 1.77 D and 1.63 D respectively. The benzene ring appears to have undergone a distortion, if the C(sp²)–F bond length is assumed to be 135 pm.