The measurement of the rate of recombination of hydrogen atoms at room temperature by means of e. s. r. spectroscopy

Abstract

Electron spin resonance spectroscopy has been used to determine the absolute concentrations of hydrogen atoms in a gas-flow system at room temperature and at total pressures between 1 and 10 Torr. The kinetics of the decay of hydrogen atoms in the presence of undissociated molecular hydrogen have been extensively analysed on the basis of a statistical treatment of errors for a model which includes first- and second-order decay processes and axial diffusion of the atoms. Care has been taken to consider the effects of high (up to about 20%) dissociation of hydrogen, of viscous pressure drop along the reaction tube, and of other possible decay processes. The predominant rate of removal of hydrogen atoms was by the reaction K 2 H+H+H 2 →H 2 +H 2 , and the value of k 2 was 2·7±0·4x10 15 cm 6 mole -2 s -1 . A small contribution from a first-order reaction K 1 H→ 1 / 2 H 2 (presumably a wall reaction) was also found. The rate constant, k 1, was 0·21±0·15s -1 , which corresponds, in the case of a wall process, to a wall efficiency of 6·5±4·6x10 -7 . No evidence could be found for the presence of the third-order process K 2 H+H+H→H 2 +H, and an upper limit for k 3 could therefore be set at 5·0x1015 cm 6 mole -2 s -1