Someone writes: "a forbidden transition never happens

PHYSICS · Multi-part · Fermi University Physics · Atomic, Molecular & Optical Physics · One-electron atoms and the origins of atomic structure · Radiative transitions, external fields and collisions

Reading the Spectrum, Ch Radial functions, orbital size and Rydberg states

Problem

Someone writes: "a forbidden transition never happens, so a hydrogen atom in the

2s

state can never decay to

1s

." The measured radiative lifetime of

2s

0.12\,\mathrm{s}

and that of

2p

1.6\,\mathrm{ns}

. ((a)) Explain, using the selection rule

\Delta l = \pm1

, why

2s \to 1s

is called forbidden. ((b)) Compute the ratio of the

2s

lifetime to the

2p

lifetime. ((c)) Say what the size of this ratio tells you about whether the claim above is correct.

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