Hydrogen atoms pressure measurement

Using either of the above approaches we have measured the thermal rate constants for some 40 hydrogen atom and proton transfer reactions. The results are tabulated in Table II where the thermal rate constants are compared with the rate constants obtained at 10.5 volt cm.-1 (3.7 e.v. exit energy) either by the usual method of pressure variation or for concurrent reactions by the ratio-plot technique outlined in previous publications (14, 17, 36). The ion source temperature during these measurements was about 310°K. Table II also includes the thermal rate constants measured by others (12, 13, 33, 39) using similar pulsing techniques. 

The chemically realistic simulations we are discussing have been performed using a united atom representation of PB, which leads to the question How does one actually measure a CH vector reorientation for such a model The answer to this question is to use the trick we discussed in the analysis of the pressure dependence of the melt structure factor of PB. Hydrogen atoms are placed on the backbone carbons at their mechanical equilibrium positions for each structure that has been sampled along the MD trajectory. The CH vector dynamics we are showing in Figure 16 is solely from the backbone reorientations of the chain. 

Bulewicz and Sugden67 measured k16 to be 6.0 + 3.0 x 10 M-1 sec-1 by monitoring the hydrogen-atom concentration in fuel-rich flat flames of H2, Na, and 02 at 1 -atm total pressure and 1600-2000°K. Under these conditions H, NO, and HNO were in equilibrium, and HNO emission was observed. They were also able to monitor the reaction... 

The rapid progress in recent years in the spectroscopy of the hydrogen atom has renewed pressure for a much better optical frequency standard. This in itself would not be enough to solve the measurement problem. New techniques of comparing optical frequencies are needed. He have developed methods of modulating lasers which can be used for frequency differences in excess of 2THz. 

At each temperature successive additions of hydrogen were made and the equilibrium pressures measured. Equilibrium was reached in minutes at temperatures above 700° C., but several hours were required at lower temperatures. Additions of hydrogen were continued until the amount of hydrogen absorbed per gram of zirconium approximated 60 atomic %. The volume of hydrogen taken up by the sample was determined as the difference between that added and the volume remaining in the reaction system at equilibrium. Corrections were made for the differences in manifold temperatures encountered during the experiments. 

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