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

Quenching of individual metastable states of antiprotonic helium (<f>p¯He+</f>) 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 <f>p¯He+</f> states <f>(n,l)</f> = (37, 34), (38, 35), and (38, 37) in the reactions [<f>p¯He+</f>](n,l) + H2 and [<f>p¯He+</f>](n,l) + D2 was investigated in the temperature range of 25–300 K. Significant quantum tunnelling effects were revealed at low temperatures and <f>(n,l)</f>-dependent reaction barriers were deduced, in good agreement with recent theoretical calculations. [Copyright &y& Elsevier]