LASER SPECTROSCOPIC STUDIES OF STATE-DEPENDENT COLLISIONAL QUENCHING OF THE LIFETIMES OF METASTABLE ANTIPROTONIC HELIUM-ATOMS (VOL A57, PG 1698, 1998)

A laser spectroscopic method was developed to directly observe the lif etimes of individual states in metastable antiprotonic helium atoms (( p) over bar He-4(+)). Collisional effects with surrounding helium atom s were studied in cryogenic gas targets at pressures between 0.1 and 9 .0 bars and at temperatures between 5.5 and 7.0 K. The metastable stat e (n, l) = (39, 35) showed a lifetime of 1.5 mu s, regardless of densi ty, whereas the lifetime of the energetically lower-lying state (37, 3 4) was found to shorten from 1.3 to 0.1 mu s with increasing density. The lifetimes of the states (38, 34) and (36, 33) were determined to b e 10 ns and 5 ns, respectively, showing the effects of the internal Au ger process. When extrapolated to zero density, the measured lifetimes agreed with the results of calculations for the radiative and Auger w idths. Using the fact that the state (37,34) becomes short lived at hi gh density, the resonance (38, 35) --> (37, 34) at a wavelength of 529 .62 nm was detected. [S1050-2947(98)01203-7].