Abstract
The secular equations with angular dependence are derived in terms of the FG matrix system representing the normal vibrations associated with the trigonal bipyramidal model of C3v symmetry. A normal‐coordinate analysis of PCl4F and CF3PCl4 both of C3v symmetry is given based on recent infrared and Raman data. The symmetry coordinates adequately represent the normal modes except for ν4, ν6, and ν7 where appreciable mixing is indicated.