An electron in protium can absorb a photon and jump to an orbit of higher energy. Is an analogous procedure possible for the nucleus of protium (a single proton)?

Can this nucleus be in an excited state? Since it consists of a single proton I can imagine that the excitation (if possible) must take place on the level of quarks.

So maybe the question should be whether quarks in protium can "jump" to states of higher energy.

PS: If you are not familiar with name Protium - it is an isotope of hydrogen with no neutrons: ${^{1}_{1}H}$. See link in the comment or https://en.wikipedia.org/wiki/Isotopes_of_hydrogen.

  • $\begingroup$ Protons can be excited to higher spin states. Would that count as an excited nucleus? $\endgroup$ Mar 8 at 14:54

3 Answers 3


As other answers have noted, a proton can be excited into many other states such as the $\Delta(1232)$ or N$(1520)$, but for clarity it is perhaps worth noting that a protium atom cannot have its nucleus in an excited state.

All proton excited states have lifetimes $\sim 10^{-23}$ seconds, far shorter than the timescale ($\sim\hbar/m_ec^2\alpha \sim 10^{-19}$ seconds) for stable electron orbitals to form. Long before a stable protium atom with an excited proton nucleus can form, that excited nucleus will have decayed.

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    $\begingroup$ Moreover, the energy to excite a proton is always more than $10^{7}$ times the ionization energy of hydrogen. It would be virtually impossible to excite the nucleus into a $\Delta$ or $N^{*}$ without blowing away the electron. $\endgroup$
    – Buzz
    Mar 9 at 5:55
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    $\begingroup$ That is what I thought too. My question was not about free proton but about a protium atom. So other two answer are a little bit misleading because they did not mention this. Therefore I changed the excepted answer to this one. But other two answers were helpful too, there is no doubt about it. $\endgroup$ Mar 9 at 8:34

The nucleus of protium, essentially a single proton, does not exhibit excited states typical of nuclei with multiple nucleons due to its lack of internal structure (it's a single proton). Nuclei with multiple nucleons, unlike protium, can undergo excited states because their internal structure allows for various configurations of protons and neutrons within the nuclear potential.

However, in high-energy physics, the quarks within a proton can reach higher energy levels, leading to the formation of particle resonances such as Delta ($\Delta$) baryons and N resonances (N*), composed of three quarks (u or d quarks) in excited configurations.

For instance, $\Delta$ baryons include $\Delta^{++}$ (uuu), $\Delta^{+}$ (uud), $\Delta^{0}$ (udd), and $\Delta^{-}$ (ddd), each with a mass of about $1232 \, \text{MeV}/c^2$ and with an intrinsic spin of $\frac{3}{2}, \frac{5}{2}, \frac{7}{2}, \ldots$ (in half-integer units) and isospin of $\frac{3}{2}$ with possible projections of isospin of $\pm \frac{1}{2}$, or $\pm \frac{3}{2}$.

You can read more about this from the Particle Data Group here and in this Wikipedia article.


You can excite a proton to a higher state in many ways. Presumably, you would restrict the choice to baryons that look like a proton (at least the same charge) and that would decay back to a proton.

On the website of the Particle Data Group you can find them all. Maybe the N1440, or the N1710? Of course, you can also make your choice on Wikipedia (But the renowned Particle Data Group is of course more reputable and reliable.)


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