Diffusion of hydrogen atoms in spherical vessels

Abstract

A previously developed model for active species concentration profiles in infinite cylindrical systems has been extended to include the spherical system. The model couples the processes of diffusion to and reaction a t the wall. Predictions of time buildup under conditions of homogeneous production by light, and time decay after extinguishing the light source, are made for H atoms. Such predictions require a knowledge of the wall recombination coefficient and the binary diffusion coefficient for H in heat bath gas. The model is experimentally tested by measuring the first-order decay constants of H at room temperature in various pressures (10-1500 tom) of six heat bath gases. The atomic concentration is monitored by Lyman-a absorption photometry. The results show good agreement with model predictions in the various heat bath gases up to -400 torr and depend only on one parameter, y, the recombination coefficient. This should be contrasted with the earlier work where slight variation in y was invoked. The rate constants at pressures higher than 400 torr are consistently higher than model predictions.

Elastic and vibrationally inelastic slow collisions: H + H2, H++ H2

“…In the energy range considered, since the elastic differential cross section is strongly peaked in the forward direction, the momentum transfer cross section is always significantly smaller than the integral elastic cross section. For H+H 2 the data available for comparison with our results are those recommended by Phelps [3] for the momentum transfer cross section, obtained by interpolation of the measured data of Lynch and Michael [22] at about 0.1 eV and theoretical data of Newman et al [23] for energies above 500 eV. For collision energies below 1 eV the Phelps data are in good agreement with ours (within 20%).…”

Determination of the Rate Constant for the NH2(X2B1) + NH2(X2B1) Recombination Reaction with Collision Partners He, Ne, Ar, and N2at Low Pressures and 296 K. Part 1

“…Using this method, the calculated D 12 (NH 2 ) was 1.3 times larger than D 12 (NH 3 ). The diffusion volume for H atoms was determined from the D 12 (H) measured by Lynch and Michael in several inert gases. This D 12 (H) differed from Fuller et al’s estimate by only 10%.…”

Determination of the Rate Constant for the NH2(X2B1) + NH2(X2B1) Reaction at Low Pressure and 293 K

“…The binary diffusion constants were calculated using the procedure of Fuller et al, and the Geom factor was determined from the measured k diff NH3 and calculated D 12 NH3 . The value of D 12 H was taken from the experimental measurements of Lynch and Michael . As noted above, reaction was the only reaction that contributed to the production or removal of NH 3 so that diffusion of NH 3 from the region outside the photolysis region was the only significant process that contributed to the replenishment of the NH 3 concentration.…”