A Hydrogen Isotope of Mass 2 and its Concentration

In a recent paper Birge and Menzel pointed out that if hydrogen had an isotope with mass number two present to the extent of one part in 4500, it would explain the discrepancy which exists between the atomic weights of hydrogen as determined chemically and with the mass spectrograph, when reduced to the same standard. Systematic arrangements of atomic nuclei require the existence of isotopes of hydrogen ${\mathrm{H}}^2$ and ${\mathrm{H}}^3$ and helium ${\mathrm{He}}^5$ to give them a completed appearance when they are extra-polated to the limit of nuclei with small proton and electron numbers. An isotope of hydrogen with mass number two has been found present to the extent of one part in about 4000 in ordinary hydrogen; no evidence for ${\mathrm{H}}^3$ was obtained. The vapor pressures of pure crystals containing only a single species of the isotopic molecules ${\mathrm{H}}^1$ ${\mathrm{H}}^1$, ${\mathrm{H}}^1$ ${\mathrm{H}}^2$, ${\mathrm{H}}^1$ ${\mathrm{H}}^3$ were calculated after postulating: (1) that the rotational and vibrational energies of the molecules are the same in the solid and gaseous states; (2) that in the Debye theory of the solid state, the $\Theta \text{'}\mathrm{s}$ are inversely proportional to the square roots of the molecular masses; (3) that the free energy of the gas is given by the free energy equation of an ideal monatomic gas; and (4) that there is a zero point lattice energy equal to $\left(\frac{9}{8}\right)R\Theta$ per mole. The calculated vapor pressures of the three isotopic molecules in equilibrium with their solids at the triple point for ordinary hydrogen are in the ratio $p_{11}:p_{12}:p_{13}=1:0.37:0.29\mathrm{}$. The isotope was concentrated in three samples of gas by evaporating large quantities of liquid hydrogen and collecting the gas which evaporated from the last two or three cc. Sample I was collected from the end portion of six liters evaporated at atmospheric pressure and samples II and III from four liters, each, evaporated at a pressure only a few millimeters above the triple point.