Low temperature behaviour of collisions between antiprotonic helium and hydrogenic molecules and an indication of the Wigner threshold law

The temperature dependence of the quenching cross section of the long-lived metastable state (n, l) = (39, 35) of antiprotonic helium, in collisions with deuterium molecules, has been measured. It was found that it increases slightly with decreasing temperature, indicating the 1/v Wigner threshold law of exothermic reactions involving neutral particles.