Atomic spectrum:

This 'finite' or the natural width of the atomic spectrum results from a number of phenomena. These are described below.

•  Uncertainty or Heisenberg broadening: That arises because of the uncertainty in the energies of the excited state.

•  Collisional broadening: It is because of the distortion of the outer energy levels arising as a consequence of the collision with other atoms.

•  Doppler broadening: It is because of the shift in the frequencies of the emitted photon due to relative motion with respect to the detector.

The details of these phenomena could be acquired from any of the standard text books on spectroscopy. A few of the books are listed at the end of the Block.