Diffusion and Heterogeneous Reaction. XI. Diffusion Coefficient Measurements for Gas Mixture of Atomic and Molecular Hydrogen

The multicomponent diffusion coefficient $D_{{\mathrm{H,\; H}}_2}$ has been evaluated from measurements of the relative atom density in a semi‐infinite catalytic cylinder as a function of (a) distance from the atom source under steady‐state conditions, and (b) time during the transient condition associated with removal of the atom source after attainment of steady state. An electron spin resonance spectrometer was employed for atom‐density measurements and a radio‐frequency discharge for atom production in the total gas‐pressure range from 0.85 to 2.6 torr. The value for the diffusion coefficient was found to be $D_{{\mathrm{H,\; H}}_2}\text{\hspace{0.17em}=\hspace{0.17em}1.8\hspace{0.17em}±\hspace{0.17em}0.13}{\mathrm{cm}}^2{\sec }^{\text{−1}}$ at 1 atm and 293° ± 3°K. Experimental data for the variation of $D_{{\mathrm{H,\; H}}_2}$ as a function of temperature (293° to 719°K) are analyzed in terms of different interaction potentials for the atom–molecule collision.