Shock Tube Determination of Dissociation Rates of Hydrogen

The rate of dissociation of hydrogen was determined in noble gas‐H₂ mixtures over the temperature range 2800° to 5000°K by density measurements in incident shock waves. An x‐ray densitometer was used to measure the density profile produced by the shock wave and the dissociation process. The experimental density profiles were compared with calculated profiles which extended from the shock to the equilibrium region to determine the dissociation rates. The three reactions considered were $${\mathrm{H}}_2+\mathrm{M}\rightleftharpoons {\displaystyle {lim}_{k_r}^{k_d}}2\mathrm{H}+\mathrm{M},$$ where M can be Xe, H₂, and H. The values and error limits of k_r=k_d/K for these third bodies in cc² mole^—2 sec^—1 are 1.5×10¹⁸T^—1±30%, 3×10¹⁸T^—1±50%, and 1×10¹⁹T^—1±50% respectively. The third body efficiencies of H₂ and H relative to Xe are 2 and 7. Kr and Ar were found to have the same efficiency as Xe in the hydrogen dissociation process. The temperature dependence of the recombination coefficient could not be determined in these measurements, so the T^—1 was arbitrarily selected for all species. These rate coefficients are approximately a factor of 2 larger than the corresponding numbers for oxygen.