A spectrum band composed of molecules which is usually found in the visible or the ultraviolet because of the electron transition taking place with the molecule.

1. A spectrum characteristic of molecules that consists of bands of spectral lines corresponding to electron transitions accompanied by vibrational or rotational transitions.
2. Bands of spectral lines connected with a change of electronic state of a molecule.

Each band is corresponding to vibrational energies in the initial and final conditions and each band consists of numerous rotational lines.