OBSERVATION OF STRUCTURE IN DIFFERENTIAL TRANSFER IONIZATION OF ARGONATOMS BY POSITRONS

In an e(+)-Ar crossed-beam experiment with positrons of 75 eV energy, we studied differential positronium (Ps) formation in the vicinity of the Thomas angle theta(Th)(Ps) = 45 degrees, searching for a Thomas re sonance. Our experiment distinguishes two reactions: (1) the transfer Ar(e(+),Ps)Ari and (2) the transfer ionization Ar(e(+),e(-)PsAr++. The angular dependence of transfer shows no statistically significant str ucture. Unexpectedly, however, we discovered a distinct minimum in the angular dependence of transfer ionization right at 45 degrees.