ELECTRIC-FIELD EFFECTS ON H- PHOTODETACHMENT PARTIAL CROSS-SECTIONS ABOVE 13.4 EV

When static electric fields (F less-than-or-equal-to 90 kV/cm) were applied to the H- photodetachment interaction region, new structure and lowered thresholds for production of neutral hydrogen were observed. Relative partial cross sections were measured by detection of excited states of the fragment neutral hydrogen atom H(N = 4, 5, or 6) resulting from laser interaction with relativistic H- ions. Downward shifts in the onset of excited hydrogen production are observed to increase with field strength, and agree with a recent hyperspherical coordinate interpretation of Zhou and Lin [Phys. Rev. Lett. 69, 3294 (1992)]. Field-induced window-type resonance structure is observed both below and above the zero-field threshold (ZFT) energy. Quenching of high-lying autoionizing states was also monitored, providing evidence of field-induced tunneling by resonances lying just below the associated ZFT.