Isotope effects on antiproton and muon capture by hydrogen and deuterium atoms and molecules

Cross sections for capture of the antiproton ((p) over bar) and negative mu on (mu(-)) by the H-2 and D-2 molecules are calculated using fermion molecu lar dynamics (FMD). All the cross sections are significantly larger than th ose fur capture by the corresponding atom, also evaluated by the FMD method . The largest molecular cross sections are obtained when the negative proje ctile mass best matches the nuclear mass in the molecular target, thus for (p) over bar + H-2. The vibrational degree of freedom is shown to be most i mportant in distinguishing the four reactions, but the effects of rotations , two-center electronic charge distribution, and nonadiabaticity are also s ignificant. The predicted initial capture fractions (i.e., not taking subse quent transfer into account) in a H-2 + D-2 mixture are P-capt((p))/P-capt( (d))= qc(p)/c(d), where q = 1.585 for (p) over bar and q = 1.186 for mu(-) independent of c(p) and c(d). The energy-dependent quantum-number distribut ions of the exotic atoms formed, the angular distributions of antiprotonic atoms, and the initial kinetic energies of muonic atoms are also presented. [S1050-2947(99)06602-0].