The ortho-para conversion of hydrogen molecules oscillating inside tetrahedral cages of silicon compounds relies on the interaction of the nuclear protons with the silicon electrons. At each collision against the cage hard walls, the electron repulsion changes the molecular rotation while projecting a valence electron in the antibonding molecular state dressed by a group of conduction ones. That "bridge" facilitates the hyperfine contact of the electrons with the protons. At room temperature, the angular momentum transfer is enhanced by electron fluctuations that overcome the silicon gap and accelerate the nuclear rates by more than one order of magnitude. (C) 2016 Elsevier B.V. All rights reserved.