QUENCHING OF METASTABLE STATES OF ANTIPROTONIC HELIUM-ATOMS BY COLLISIONS WITH H-2-MOLECULES

Laser resonance transitions between normally metastable slates of anti protonic helium atoms were induced making use of state dependent quenc hing effects caused by trace admixtures of H-2 to the target helium ga s. With this method of ''H-2-assisted inverse resonances'' the decay r ates of the stales (n, l)= (39,l), l = 36,37,38, and (38,l), l = 35,36 ,37 of (p) over bar He+ were determined as a function of the H-2 admix ture. The quenching cross sections at 30 K deduced therefrom for the s tates with n = 39 were found to be of the order of the geometrical cro ss section for (p) over bar He+-H-2 collisons (2 10-(15) cm(2)), with a moderate decrease with increasing I. Within a given cascade with con stant v = n - l - 1, the quenching cross sections for states with n = 38 are smaller by a factor of 4-6 than those for states with n = 39. ( C) 1998 American Institute of Physics.