Question

Why do molecules show band spectra rather than line spectra?

Answer 1

Line spectra are also called atomic spectra because the lines represent wavelengths radiated from atoms when electrons change from one energy level to another. ... Band spectra, or molecular spectra, are produced by molecules radiating their rotational or vibrational energies, or both simultaneously.

Answer 2

Introduction about the topic..

A line spectrum is a set of discrete wavelengths from gaseous atoms, whereas a band spectrum is produced by molecules, which consists of a series of closely spaced lines separated by dark spaces called bands.

Talking about the question....

If a molecule is irradiated, apart from the excitation - there will be additionally rotational or vibrational movements taking place. This is what accounts to the several line spectrum as a band spectrum.

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