The figure below shows the visible part of the spectrum for severalatomic or molecular sources. For
Hydrogen, we mainly see the Balmer series, with a line from Paschen-Bach. The spectra of different
atoms are quite distinct. Molecules have many other types of excitations and can produce many
frequencies of light.
2.4.1 The Bohr Atom*
Bohr postulated that electrons orbited the nucleus like planets orbiting the sun. He managed to fit
the data for Hydrogen by postulating thatelectrons orbited the nucleus in circular orbits,