In stellar nucleosynthesis, how is helium produced from a protium atom that has no neutrons?

  • $\begingroup$ It is a good question, but I think it might be better off being regarded as nuclear physics. Nuclear chemistry is chemistry of radioactive and nuclear materials and some other things. It has been argued that it is "the study of radioactivity using chemistry and the study of chemistry using radioactivity". $\endgroup$ Aug 27 '18 at 16:06

In the process of stellar nucleosynthesis, the helium comes from deuterium ($\ce{^2H}$) produced through the Proton–proton chain reaction (P-P 1).

In P-P 1, two proton ($\ce{^1H^+}$) atoms fuse to form one deuterium atom, as well as a positron ($\ce{e^+}$) and a electron neutrino ($\ce{v_e}$).
One deuterium atom and one protium atom fuse, forming one helion ($\ce{^3He}$) atom and releasing a photon as a gamma ray ($\ce{Y}$).
This is followed by the fusion of two helion atoms, creating an alpha particle ($\ce{a^2+}$ / $\ce{He^2+}$).

Here's a diagram from Wikimedia Commons depicting the process:

Diagram depicting Protium fusion


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