Calculation of atomic recombination in a decaying high-temperature hydrogen gas column

The temporal evolution of the concentration of atomic radicals [H] in a hig h-temperature hydrogen gas column has been evaluated, assuming an exponenti ally decaying temperature from 5000 K to 1000 K, and far constant pressures in the range from 0.125 to 2.0 bar (1 bar = 10(5) Pa). The initial concent ration [H](t=0), assumed to correspond to thermal equilibrium, would increa se with pressure, but the termolecular recombination processes also become faster with increasing pressure. As a result, high concentration of atomic radicals rapidly becomes favoured by lower gas pressure after the temperatu re has decayed for a certain rime. Also, operation at lower pressures would make the decay of [H] radicals less dependent upon the cooling rate of the gas.