[Khyati]

Can any one tell from where Pauli got to know about the spin of the electrons? What gave him the idea that electrons in the same orbital should have the opposite spins?

[cliverlong]

Can any one tell from where Pauli got to know about the spin of the electrons? What gave him the idea that electrons in the same orbital should have the opposite spins?

The following sources suggest it was Ralph Kronig

http://www.library.ethz.ch/exhibit/pauli/elektronenspin_e.html

and that Uhlenbeck and Goudsmit created a physical interpretation in terms of spin (a term not originally used by Pauli)

http://www.lorentz.leidenuniv.nl/history/spin/goudsmit.html