Triatomic Ions in Mixtures of the Hydrogen Isotopes

Abstract

A mass spectrograph analysis has been made of aged ions in mixtures of hydrogen and deuterium. The concentration of deuterium was varied from 84 percent to less than one percent. After drifting through 5 cm of gas at about 0.5 mm pressure, the ions were found to be over 95 percent triatomic; that is, H3 +, H2D+, HD2 + and D3 +. Measurement of the relative intensities of the triatomic ion peaks indicates a slightly greater number of H3 + and D3 + ions compared to H2D+ and HḊ2 + than would be expected from probability considerations if the H and D atoms behaved exactly alike. This tendency for like atoms to group together may be accounted for by taking cognizance of the proper equilibrium constant for the different types of diatomic molecules in the gas mixtures employed. There is no evidence of further preferential grouping in the formation of the triatomic ions from the primary molecular ions. The relative heights of the triatomic ion peaks may be used to determine the abundance of the isotopes in a sample of gas.