Effects of electric fields on the photodetachment cross section of the H- ion near threshold

A study is presented of the photodetachment cross section of the H- ion near the one-electron threshold in electric fields ranging from approximately 5 x 10/sup -7/ up to 2.4 x 10/sup -4/ a.u. The lowest-field data, nominally at zero field, are consistent with the Wigner threshold law for p-wave processes. At larger field values, photodetachment using σpolarized laser light displays the expected lowering of apparent threshold and evidence of tunneling. Using π-polarized light, the same features are seen with the additional feature of oscillations superimposed on the cross section. Three complementary explanations are presented for the oscillations