Is the energy of the photon coming in greater than or less than the energy of the electronic transition?

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Is the energy of the photon coming in greater than or less than the energy of the electronic transition?

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Answer 1 · 2017-06-22T23:47:15

Neither. It has the energy given by the difference in energy, $E_{f} - E_{i}$ $E_f - E_i$ .

When photons are absorbed to excite an electron from initial energy $E_{i}$ $E_i$ to final energy $E_{f}$ $E_f$ , they must account for the difference in energy, $DeltaE = E_f - E_i$ in order for the electron to transition upwards by that energy.

Suppose you wanted to go from $E_1$ to $E_2$ in the hydrogen atom. Then,

$E_"photon" = DeltaE = -"13.6 eV"(1/2^2 - 1/1^2)$

would be the energy that the one absorbed photon needs to be in order to get the electron from $n = 1$ (where $E_1 = -"13.6 eV"$ ) to $n = 2$ (where $E_2 = -"3.4 eV"$ ).

![ astro.unl.edu )

If you had $"13.6 eV"$ for that photon, you wouldn't be going from $E_1$ to $E_2$ ; you'd be going way past that, since the difference is only $+"10.2 eV"$ . And since the difference is that, you can't have $"3.4 eV"$ available and bridge that gap.

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Is the energy of the photon coming in greater than or less than the energy of the electronic transition?

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