Investigation of the chemical reactions H + H 2 and H + D 2 by a hydrogen maser

Abstract

The rate constants of the gaseous chemical reaction H + H 2 → H 2 + H(l) ( k = 4.4 ± 0.5 × 10 −14 cm 3/molec. s at T = 440 K and 8.2 = 0.81 × 10 −14 cm 3/molec. s at T = 470 K) and H + D 2 → HD + D (H) ( k = 2.35 ± 0.3 × 10 −14 cm 3/molec. s at T = 470 K) were measured by a method using an H-maser as a highly sensitive relaxometer for hyperfine levels of hydrogen atoms. From the ratio between the reaction rate constant and the rate constant for the coherence change induced by collision of the partners - which appeared to be 4 3 for reaction (1) and 1.0 for reaction (II) - the conclusion was made that the change in nuclear magnetic states of the partners ( ortho-para conversion for reaction (I)) occurs by transitions of the heavy particle only, i.e., as a result of the chemical reaction. Theoretical analysis of the changes in population of the H-atom hyperfine levels and the H 2-molecule nuclear sublevels as a result of reaction (i) was carried out under the assumption of a small perturbation of the magnetic momenta. For the linear and triangular H 3 complexes it was found that the rate constant for reaction (I) is related to that of the complex formation as k H = 1 2 kP L c and k H = 2 3 k T c, respectively.