A FRESH STUDY OF SOME TRIGONAL BIPYRAMIDAL MOLECULES

In a five atom XY(4) molecule if two Y atoms are replaced by Z atoms t he symmetry is lowered from T-d to C-2v. As a result the selection rul es are changed. Z(2)XY(2) molecules have eight infrared active vibrati ons and all are Raman active, and the distribution is Gamma=4a(1),(IR, R)+A(2)(R)+2B(1)(IR, R)+2B(2)(IR, R). Early infrared studies on sulfu ryl halides and chromyl halides led to some controversies regarding th e structure, but Raman spectra of them have conclusively established t hat the structure possesses C-2v symmetry. Such molecules have two pla nes of symmetry, one containing Z and X atoms and the other containing X and Y atoms.