2838.     ROBERTS, J. K.  Adsorption of Hydrogen on Tungsten.  Proc. Roy. Soc. (London), vol. 152, A, 1935, pp. 445-463; Chem. Abs., vol. 30, 1936, p. 1630.

        Method is described for studying the adsorption of H2 on a bare W surface, which depends on the fact that the accommodation coefficient for Ne is considerably greater for a surface covered with a film of adsorbed gas than for pure W.  It is shown that on a clean W surface chemisorption of H2 occurs very rapidly at temperatures as low as 79 K., saturation of the surface taking place at a partial pressure of 10-4 mm. or less.  The heat of adsorption as measured on a single fine wire varies from 45,000 cal./mol. for the 1st H2 mol. to 18,000 for the last portion becoming adsorbed.  The amount of H2 required to form a unimolecular layer is consistent with the adsorption of H as atoms.  The film is stable for heating times of about 1 min. up to about 700 K.  Calculations show the dipole moment/adsorbed atom to be 1.94 x 10-16 e.s.u. and the change in work function resulting from covering the surface with a complete film to be 5.2 v.  The rapidly occurring chemisorption of H2 on the W surface differs from the more slowly occurring activated adsorption.  The accommodation coefficient of Ne at 79 K. is 0.32 on a W surface covered with a layer of chemisorbed H2 compared to about 0.1 for bare W; at 295 K. the coefficients are, respectively, 0.17 and about 0.08.