Abstract
AbstractThe unpaired electrons of the solid free radical αα'‐diphenyl‐β‐picryl‐hydrazyl (D.P.P.H.) convert parahydrogen at low temperatures. The mechanism is the paramagnetic physical mechanism, as absence of the hydrogen‐deuterium exchange reaction rules out dissociative chemisorption of hydrogen molecules by the free valencies. This confirms earlier work. In extension of this, the mobility of the free radical electrons in the solid are determined by A.C. and D.C. conductance measurements. Hydrogen, nitrogen and oxygen do not effect this conductance and are therefore probably not chemisorbed. Hydrogen in the presence of a palladium film lowers the A.C. conductance of a D.P.P.H. film indicating covalency formation with the H atom, a partial electron transfer H ← D.P.P.H. Hydrogen sulphide raises the D.C. conductance of D.P.P.H. powder, suggesting a lowering of intercrystalline barriers by an electron transfer H2S → D.P.P.H. A film of D.P.P.H. deposited on a film of Al or Pd raises the D.C. resistance of the latter, suggesting electron transfer (Al or Pd) ← D.P.P.H.