Chapter 14, Problem 14.74E

Interpretation Introduction

Interpretation:

The irreducible representation labels for the vibrational modes of diacetylene $\text{HC}\equiv \text{C}-\text{C}\equiv \text{CH}$ are to be stated. The vibrational mode that is IR active for symmetry reasons is to be stated.

Concept introduction:

The complex vibrations exhibit by the polyatomic molecule is known as normal modes of vibrations. The vibrational modes of a molecule are IR or Raman active. If a molecule has centre of symmetry, then the modes which are IR-active will be Raman inactive and the modes that are IR-inactive will be Raman active.