In the Bohr atomic model, electrons move between shells having angular momentum L_n = n h_bar where n is the shell number and the difference in shell energies E_n2-E_n1 matches the Rydberg energy of the emitted or absorbed photon.(adsbygoogle = window.adsbygoogle || []).push({});

My question is: what hapened to the angular momentum (n2-n1)h_bar?

For this to be carried in or out by the "massless" photon (assuming we abandon Bohr classicism for relativistic 4-vector momentae) would require the photon trajectory to be at a precisely correct angle.

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# Bohr Model missing momentum question

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