Quantum tunnelling effects revealed in collisions of antiprotonic helium with hydrogenic molecules at low temperatures

Quenching of individual metastable states of antiprotonic helium (p̄He+) in collisions with H2 and D2 in gas phase was studied using a laser-resonance method at CERN’s Antiproton Decelerator. The temperature dependence of the quenching cross-sections of the p̄He+ states (n,l) = (37, 34), (38, 35), and (38, 37) in the reactions [p̄He+](n,l) + H2 and [p̄He+](n,l) + D2 was investigated in the temperature range of 25–300 K. Significant quantum tunnelling effects were revealed at low temperatures and (n,l)-dependent reaction barriers were deduced, in good agreement with recent theoretical calculations.