Coriolis interactions and infrared intensities in fluoroform

Infrared intensities of the fundamental bands of the CHF3 molecule were remeasured. The Coriolis interaction between ν3 and ν5 bands as well as that between ν6 and ν5 bands was analyzed to determine the sign of the perturbation. As a result, the relative signs of all the (∂p/∂Qi)’s in this molecule have been determined without using the CNDO/2 method or an ab initio calculation. An empirical rule on the sign of the CF bond intensity parameters is proposed by the name of ’’CF-bond criteria’’, according to which a negative dipole moment is enhanced in the direction of the displacements of the F atoms in both the CF stretching and CF deformation modes. Further, a possibility is suggested to extend this rule to all halogen atoms.