DISSOCIATIVE RECOMBINATION STUDIES OF AR-2(-OF-FLIGHT SPECTROSCOPY() BY TIME)

From time-of-flight spectra of metastable Ar atoms emerging from sust ained discharges in Ar, we observe discrete nonthermal peaks due to ex cited products of dissociative recombination (DR) of Ar-2(+) formed by reactions in the discharge. These peaks are in addition to the expect ed Boltzmann distributions of metastable atoms from direct excitation by fast primary electrons. From the peak velocities, and thus the kine tic energies released in the dissociation, the DR product states are u niquely determined, regardless of subsequent radiation. As we have pre viously found from Kr-2(+) [A. Barrios et al., Phys. Rev. Lett. 69, 13 48 (1992)], most of the excited DR products are (n + 1)s states, but A r-2(+) also yields smaller amounts of 4p and 3d states. We have also r ecently shown [G. B. Ramos et al., Phys. Rev. A 51, 2945 (1995)] that, surprisingly, in studies of Ne-2(+) and Ar-2(+) DR, a substantial but undetermined fraction of reactions go to a purely ground-state channe l. In addition, we have found that under certain conditions in Ar disc harges, the relative amount of the higher excited-state products, incl uding 4p, 3d, 5s, and 5p can be dramatically influenced. The velocity peaks also become narrower than expected from the thermal distribution of the parent Ar-2(+) as the energy level in the product atom increas es. These studies in argon discharges have included variations in sour ce pressure, discharge voltage, and strength of the axial magnetic fie ld.