Collisional quenching of metastable states of antiprotonic helium by hydrogen and deuterium molecules

摘要

The quenching of metastable states of antiprotonic helium by collisions with hydrogen and deuterium molecules was studied. A systematic investigation of the delayed annihilation time spectra at various H_2 and D_2 admixture ratios at the ppm level revealed characteristic changes of their shape, which indicated a strong principal and orbital quantum number dependent quenching of levels in both cases. Applying a laser spectroscopy technique to measure the lifetimes of individual states and cascades we deduced H_2 and D_2 quenching cross-sections for the states (n,l) = (39,35) and (37,34). These cross-sections establish for D_2 molecules the strong increase of the quenching efficiency with increasing principal quantum number n of the state under investigation previously reported for the case of H_2 admixtures. Our experiments indicate that the low-n state (37,34) is somewhat less affected by D_2 than by H_2, while the high-n state (39,35) is equally quenched by both isotopes.