Infrared intensities of the fundamental bands of the CHF3molecule were remeasured. The Coriolis interaction between ngr;3and ngr;5bands as well as that between ngr;6and ngr;5bands was analyzed to determine the sign of the perturbation. As a result, the relative signs of all the (part;p/part;Qi)rsquo;s in this molecule have been determined without using the CNDO/2 method or anabinitiocalculation. An empirical rule on the sign of the CF bond intensity parameters is proposed by the name of rsquo;rsquo;CFhyphen;bond criteriarsquo;rsquo;, 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.
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