[Physics] Energy shift between hydrogen and deuterium

atomsquantum mechanicsspectroscopy

Stated: The atomic spectra of hydrogen and deuterium are similar however shifted in energies.

So im trying to explain why it is that the emission lines are shifted and how they are shifted.

Since the nucleus of deuterium contains both a proton and a neutron its notably heavier than the nuclueus of hydrogen, which only contains a proton. And since the transition energy is given by following equation:
$E_i-E_f = \frac{\mu_xZ^2e^4}{(4\pi\varepsilon_0)^22h^2}\left[\frac {1}{n_f^2}-\frac {1}{n_i^2}\right]$, where $\mu_x $ is the reduced mass of Atom $X$. its clear that the energy varies with the atom mass.

But i dont really know how to tackle the second part of my problem i.e. explaining how they are shifted.

Thank you in advance!

Best Answer

Consider the ratio of their shifts in energy. Since all the numbers are the same except for the reduced mass you are looking at something like: $$ \frac{(E_i -E_f)_p}{(E_i -E_f)_d}=\frac{\mu_p}{\mu_d}=\frac{m_p m_e(m_d +m_e)}{(m_p +m_e)m_d m_e} $$ If we cancel the $m_e$ and then pull a $m_d$ out of the top and a $m_p$ out of the bottom we get $$ \frac{(E_i -E_f)_p}{(E_i -E_f)_d}=\frac{(1+\frac{m_e}{m_d})}{(1+\frac{m_e}{m_p})} $$ I hope this helps.

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