We consider several nuclear fusion reactions that can take place at th
e center of the sun, which are omitted in the standard pp-chain model.
More specifically the reaction rates of the nonradiative production o
f He-3, Be-7, and B-8 nuclei in triple collisions involving electrons
are estimated within the framework of the adiabatic approximation. The
se rates are compared with those of the corresponding binary fusion re
actions.