Resonant electron attachment to oxygen molecules in dense helium gas

Measurements of the resonant attachment frequency of excess electrons to O₂ molecules in dense helium gas have been performed in the temperature range 50-100K. The attachment frequency exhibits a sharp peak at a density N_P, which has an unexpected temperature dependence. The peak shape has been simply related to the density dependence of F(E_R), the value of the energy distribution function at the resonance energy E_R. The results of the experiment indicate that resonant capture by molecular impurities can be used to get unique information on the density of states of a disordered system.