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

Abstract

Quenching of individual metastable states of antiprotonic helium ( p ̄ He + ) in collisions with H 2 and D 2 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 p ̄ He + states ( n, l) = (37, 34), (38, 35), and (38, 37) in the reactions [ p ̄ He + ] (n,l) + H 2 and [ p ̄ He + ] (n,l) + D 2 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.