# quantization of angular momentum

What is the most direct way of observation of quantization of angular momentum?

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Possible duplicates: physics.stackexchange.com/q/11197/2451 and links therein. –  Qmechanic Apr 14 at 9:55

Rotational spectroscopy seems like a pretty obvious demonstration of quantised angular momentum. If you look at the microwave absorption spectrum of a diatomic molecule (with a non-zero dipole moment) you'll find equally spaced absorption lines. These arise because the angular momentum can only change in integral jumps of $\hbar$.

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Classically you expect that the spin of the electron can be oriented along any random direction, therefore you'll see a spread of particles when they hit the photographic plate. But what they actually observed was two distinct beams of silver atoms. This was interpreted to mean that the angular momentum of an electron can have only two values: $\hbar/2$ and $-\hbar/2$.