Vibrational assignment and dipole moment derivatives of hexafluorobenzene between 4000 and 250 cm −1

Abstract

The liquid phase vibrational assignment and dipole moment derivatives of hexafluorobenzene are reported. These are obtained by fitting the imaginary molar polarizability spectrum of hexafluorobenzene to classical damped harmonic oscillator bands. Most of the observed transitions were assigned to infrared active fundamentals or binary combinations. From the active combination transitions, the wavenumbers of the inactive fundamentals were obtained. In addition, ab initio calculations at the CCD/cc-pVDZ level of theory were used to determine the harmonic force field and dipole moment derivatives of gaseous hexafluorobenzene. It was determined that in the gas phase ∂μ y / ∂s 1=−5.53 Debye Å −1, ∂μ x / ∂t 2=1.03, ∂μ x /∂β 1=0.78, and ∂μ z /∂γ 1=0.57 Debye Å −1 while in the liquid ∂μ y / ∂s 1=−4.00 Debye Å −1, ∂μ x / ∂t 2=1.27, and ∂μ x /∂b 1=0.50 Debye Å −1. ∂μ z /∂γ 1 could not be determined for the liquid phase because the fundamental is below the limits of the current measurements. The differences between the liquid and gas phase dipole moment derivatives of hexafluorobenzene were found to be consistent with the differences previously reported for benzene.