Editing Proton–proton chain (section)

===The {{nowrap|p–p IV}} (Hep) branch===
This reaction is predicted theoretically, but it has never been observed due to its rarity (about {{val|0.3|ul=ppm}} in the Sun). In this reaction, helium-3 captures a proton directly to give helium-4, with an even higher possible neutrino energy (up to {{val|18.8|u=MeV}}{{citation needed|date=June 2020}}<!--Total energy is more, like 19.795-->).

<!-- Autogenerated using Phykiformulae 0.11 by [[User:SkyLined]]
He-3 + H → He + e+ + ve + 18.23 MeV
-->:{| border="0"
|- style="height:2em;"
|{{nuclide|link=yes|helium|3}}&nbsp;||+&nbsp;||{{nuclide|link=yes|hydrogen|1}}&nbsp;||→&nbsp;||{{nuclide|link=yes|helium|4}}&nbsp;||+&nbsp;||{{SubatomicParticle|link=yes|Positron}}&nbsp;||+&nbsp;||{{math|{{SubatomicParticle|link=yes|Electron Neutrino}}}}
|}

The mass–energy relationship gives {{val|19.795|u=MeV}} for the energy released by this reaction plus the ensuing annihilation, some of which is lost to the neutrino.