Characterization of the 1De autodetaching resonance in H- and D-

We have measured the hydrogen-deuterium isotope shift in the energy of the lowest D-1(e) autodetaching resonance in the two-photon absorption spectrum of H-. The D-1(e) resonance in negative deuterium lies 2.0 +/-0.5 meV, with a possible systematic error of 0.4 meV, above the corresponding resonance in negative hydrogen when measured with respect to the ion ground state. From the isotope shift, we obtain a mass polarization of 2.4+/-1.1 meV, with a possible sytematic error of 0.8 meV, for the D-1(e) in H- under the assumption that the Fano shape parameters, q, for the two isotopes are the same. Recent theoretical calculations give the mass polarization for this resonance in H- as -0.1 meV. The generalized absolute cross section of two-photon absorption at the peak of the D-1(e) is found to be (3.2(-1.2)(+1.8))x10(-49) cm(4) s. The measured asymmetry parameters beta(2) and beta(4) of the photodetachment process are 1.9+/-1.2 and 2.21+/-0.45, respectively, consistent with a pure D-wave distribution. Upper bounds on the second recursion of the lowest S-1(e) resonance and three-photon excess photon detachment are 2.8x10(-49) cm(4) s and 3.1x10(-78) cm(6) s(2), respectively.