Stark broadening of H(-) resonances in large electric fields

Resonances in the H(-) ion near the n=2 energy of H(0) were studied in very large electric fields. Third harmonic photons (3.5 eV) from a Nd:YAG laser were Doppler tuned to produce the 11 eV photons required to excite the resonances. A magnetic field perpendicular to the H(-) velocity appeared via the Lorentz transformation as a very large electric field in the center of mass frame of reference. The magnetic fields were produced by a pulsed power supply driving a Helmholtz coil. The maximum field used (3 MV/cm) was sufficient to field ionize enough of the H(-) beam, within the 1.5 cm high field region, to saturate the detectors. The onset of field ionization was observed to be at 2.5 MV/cm. The (1)P(0) shape resonance and (1)D/sup e/ resonance were not quenched by the largest fields used. Cross sections for these resonances were measured at several lesser fields, and widths, centroid energies, and strengths for each resonance were determined. The cross section for producing H(0) (n=2) was measured for the first time and was shown that the Fano function is inadequate to describe the shape resonance.