Question

Q1) Provide the point group for the IR- or Raman-active vibrational modes using the
character tables provided below. Each point group is only represented once.

i) $\Gamma$ IR Vibration = 2B2u + B3u ______ ii) $\Gamma$ IR Vibration = 2B2 + E ______
iii) $\Gamma$ IR Vibration = 3T2 ______ iv) $\Gamma$ Raman Vibration = 2A1 + E1______
v) $\Gamma$ IR Vibration = 2A1 + E ______ vi) $\Gamma$ Raman Vibration = 2B3 ______

b) Which point group represents a centrosymmetric molecule? ___________

Answer 1

0 0 0 TiR vibration = 2Brut Bu as the molecule is centrosymmetric So Raman modes are IR inactive, ( TIR 2 B₂ + E + A2 As the molecule does not has ; Symmetry so the other modes than A are IR active as well Raman active.

c 3 Tz + T & DODA IR Sinilar way, the point group does not contains i symmetry. So symmetry. So, except A other irreducible representation are IR active . cin Raman 2A, & E, & E The term xy, or x Zx y z , xyz z 2 Raman active mode. and the torm Rn x, or, y, or Z or IR active. Rey., R2 ♡ TIR - 2 A + E & A2 AS A irreducible representation contain Rz operation, mode ( T Raman = 2Bg + Be + B + A

b) the point group D2h are centrosymmetric as it contains center of symmetrty (i).