Observation of inverse predissociation of spin-polarized atomic hydrogen at low temperatures

Measurements of the two-body recombination of spin-polarized atomic hydrogen in a magnetic field of 40 kG have been extended to temperatures above 0.5 K. The rate constant for the formation of parahydrogen shows an unexpected increase with temperature, which is explained by inverse predissociation into the $v=14\mathrm{}$, $J=4\mathrm{}$ level of ${\mathrm{H}}_2$. Data indicate the level is bound by 0.7±0.1 K.